Facebook’s IPO is causing a frenzy among investors eager to get a piece of the social networking website.

Warren Buffett’s Berkshire Hathaway built new positions in General Motors and Viacom during the first three months of 2012.

Olympics deal helps push revenues at G4S higher, but British Airways parent company IAG has seen its rating cut by JP Morgan

A deal to protect visitors to the London Olympics has helped to push G4S to the top of the FTSE 100 risers, on a calmer morning in the City after yesterday’s heavy selloff.

G4S, the world’s biggest security provider, reported a 7.5% jump in revenues for the first quarter of 2012. After ther the failed takeover of ISS last autumn, the company assured shareholders this morning that growth prospects remained good.

Based on recent contract awards, outsourcing trends and the group’s bid pipeline, the organic growth rate is expected to continue to improve during 2012.

The Olympics contract will yield £150m to G4S this year. The firm also reported strong growth in the Middle East, Latin America and Africa. Shares were up 10.1p at 276.9p, a gain of 3.7%.

The FTSE 100 was up just 9 points shortly before midday at 5474, as traders sat tight following yesterday’s 110-point slump. The blue chip index had been as high as 5507 following the news that the eurozone had not fallen into recession, before optimism eased.

David Jones, chief market strategist at IG Index, commented:

It all started so well this morning. A stronger-than-expected German GDP reading demonstrated the robustness of the eurozone’s principal economy, while French data at least confirmed that Paris had not slipped back into recession. This helped markets to gain ground, but the atmosphere remained cautious. That caution was proved well-founded as Italian GDP emerged to spoil the party, coming in below expectations, and markets promptly retreated.

In a busy morning for eurozone economic data, overall eurozone GDP for the first quarter was left unchanged at 0%, showing that the German titan was still doing its best to hold the line against a union-wide recession. Meanwhile, we are facing yet another day of Greek negotiations, but what hopes are left are already fading.

IAG, British Airways’ parent company, was the biggest faller this morning. Shares are down 4.8p at 154.5p, a drop of 3%, after a JP Morgan downgrade – from overweight to neutral. The bank warned that IAG’s Iberia operation faced “headwinds from weaker Spanish trading”, while higher-than-expected losses at recently acquired bmi also made the firm less attractive.

US search engine launches low-key credit card comparison site, but could expand into other areas

Moneysupermarket.com, the price comparison website, has dropped more than 7% on fears of growing competition, notably from Google.

Analyst David McCann at Numis noted that Google has recently launched a price comparison site, embedded in its main search results:

At the moment it is limited to credit cards, savings and current accounts. It appears to still be very much in “test mode”: it only appears on more obscure Google searches such as “credit cards uk” rather than “credit card” (suggesting that Google are not yet ready to cannibalise some of the lucrative “credit card” cost-per-click keywords) and the range of providers within each category is much more limited than incumbents offer. However, the technical capability appears to be in place and with some “look and feel” refinement, a more whole of market offering and the development of commercial relationships with providers, it does not feel a long way away from being a credible direct competitor.

McCann said around a third of Moneysupermarket’s revenue comes from visitors via Google, and any new service from the search engine giant could divert vistors from Moneysupermarket to its own site. He added:

Last year, a third of Moneysupermarket’s revenue was around £60m, which at a gross margin of 55% (including offline marketing costs), means around a £33m contribution was connected to Google. This compares to the £50m earnings, with the remaining costs being largely fixed. [So] we calculate around two-thirds of profits could be at risk.

We think it is somewhat naive, as some have suggested, that the profits at risk are limited only to the products that Google are currently testing on the site: we cannot see why Google, if serious about the venture, would not want to grow into many other channels in time. Even if it is just this direct revenue at risk (probably 5-10% of revenue), this still implies a not inconsequential 10%-20% of profit at risk.

As a result he has moved his recommendation from hold to sell. The company’s shares are currently 9.4p lower at 117.1p.

Update 14.20

The company has responded to the above comments, saying that the Google service was not a surprise and had been flagged up at its half year results last year.

It also maintains Google has been in credit card price comparison for a number of years, with little impact so far, and points out Google trials many things but sometimes decides not to go ahead. And it said it believed its product with its smart serve features gives a better outcome that Google.

Still, with the sell note from Numis, the shares are still around 7% lower at the moment.

Leading shares under pressure as Greek turmoil continues, with £28.5bn wiped off value of UK’s top companies

As markets plunged around the world on the escalating crisis in Greece, there were few bright spots for investors.

One was Invensys, the engineering group, which added 6.5p to 209p as takeover speculation refused to die down. The list of potential suitors for the business has been growing over the past few days, with Siemens, ABB, General Electric and China’s CSR all mentioned. Reports over the weekend suggested there could have been informal approaches, but there has been no comment from the company. Traders were hoping for more news when Invensys issues its final results on Thursday. Analyst Harry Philips at Oriel Securities said the company – which encompasses industrial process controls and rail – would be a manageable target for larger companies in the sector, and a bid from one major player could well prompt interest from the rest.

Overall though the FTSE 100 slumped 110 points to 5465.52, its lowest level since 22 December. Some £28.49bn was wiped off the value of Britain’s top companies, according to FTSE Group figures. With Greece still struggling to form a government in the wake of the recent inconclusive elections, and fears the country could run out of cash, there was growing talk it could exit the euro altogether. But this uncertainty – and the implications for the rest of the eurozone – has unnerved investors and prompted a sell-off of risky assets.

Banks were among the leading fallers once more, on concern about their exposure to the eurozone, with Barclays 13p lower at 189.8p, Lloyds Banking Group 1.705p lower at 29.38p and Royal Bank of Scotland down 1.11p at 21.85p.

News that China had reduced reserve requirement ratio – the amount of cash banks are required to hold as reserves – renewed worries about a slowdown in the country’s economy and sent mining shares lower. Eurasian Natural Resources Corporation ended 23.7p lower at 492.8p while BHP Billiton lost 66p to £17.98.

One of the few risers in the leading index was Severn Trent, up 11p to £17.04 as utility shares fulfilled their traditional role as a haven from the global storms.

Among the mid-caps Rank rose 6.8p to 123.5p after it confirmed it was buying 23 UK casinos from Gala Coral for £205m in cash. Jeffrey Harwood at Oriel Securities issued a buy note, saying:

This is a sensible strategic deal for Rank. The transaction should be well received by the market; the shares look attractive on a single digit PE following the deal, although there are liquidity issues relating to the 74% interest of Guoco.

Oil explorers were in focus after comments from both JP Morgan Cazenove and Deutsche Bank. Phil Corbett at Deutsche Bank said:

Sentiment towards exploration and production companies had been trending positive in 2012, fuelled by higher oil prices, mergers and acquisitions, and exploration success in East Africa. This has been derailed in recent weeks by choppy equity market conditions. However, a well stocked calendar of funded, high tariff exploration wells should hopefully maintain interest in the sector and mitigate the downside. Investors therefore have to decide whether to chase premium rated shares that have already delivered, or buy undervalued production and development with exploration in for free. With spot Brent still north of $100 a barrel, our focus is the latter.

For both Afren and Premier Oil, significant production growth in 2012 coincides with higher oil prices, delivering robust cash flow generation. We see little in either share for growth potential. For Afren, a significant re-rating of its Kurdistan assets seems likely once the export stalemate is resolved, while seeming ambivalence to its East Africa portfolio contradicts positive news flow from the region. For Premier, we see a business well capable of not only delivering its 100,000 barrel of oil equivalent per day target, but also growth from there and potential for meaningful shareholder returns. With the shares trading at a 27% discount to core net asset value, it is the cheapest stock in the sector. That cannot be justified, in our opinion, given significant value creation through the drillbit in the past decade.

Cazenove also liked the look of Afren, saying:

Once the oil price finds a level and the market de-risking ends, we would look to top up in certain names that offer near term drilling result catalysts, look under-valued after the sell-off and could be consolidation targets. Afren is our preferred name for net asset value growth potential at a reasonable valuation.

But with the markets in turmoil, Afren edged 0.7p lower at 120.8p as it announced a successful exploration well in Nigeria, while Premier slid 8.3p to 337p.

Chariot Oil and Gas halved, falling 74.25p to 75p following news that its first well in Namibia was a dry hole and was being abandoned. Peel Hunt moved its recommendation from buy to sell, while Canaccord Genuity said:

This is clearly a disappointing result. However, the pullback may offer an opportunity to take a position ahead of the farmed-out Nimrod Albian well [which is expected to begin drilling in the third quarter in the south of Namibia]. Chariot is a high risk exploration story, but in the event of success we believe the upside would be very material.

Finally Thomas Cook lost 2.25p to 19p after UBS edged its price target down from 23p to 21p and said a £1.4bn refinancing packaged to shore up the balance sheet until 2015 was just a short term fix. Meanwhile weekend reports suggested the company could go into administration if shareholders did not approve a sale and leaseback of 17 aircraft and the disposal of its HCV Spanish hotel chain. The company is holding a shareholders meeting to vote on the deals on 29 May.

But a number of investors are backing the plans. Stephen Anness, fund manager at Invesco, which holds 10.15% of Thomas Cook, said:

We wholeheartedly support the action that Thomas Cook has taken in recent months and the work that Frank Meysman and his team are doing to further stabilise the business. The successful completion of the refinancing deal has put the business in a much stronger financial position and we are confident that progress will continue to be made. We believe the board is taking the right steps to secure the future for Thomas Cook and we will be supporting the resolutions at the general meeting and we fully expect other shareholders to do so too.

A Thomas Cook source said Marathon, which holds 8.56%, and Standard Life with 4.94%, also supported the company’s proposals.

Investors unsettled by growing concerns about Greek euro exit and future growth in China

Banks and mining companies are leading the fallers in a slumping market, amid growing uncertainty about Greece’s future in the eurozone and worries about China’s economy.

As the political impasse continues in Greece, with the prospect of new elections looming, the idea that the country could exit the eurozone is gaining currency, especially as members of the European Central Bank’s governing body have been openly talking about the possibility. Any Grexit would inevitably lead to speculation about the next to depart, but more immediately, there would be concerns the country would be in danger of defaulting.

So banks are on the way down on their exposure to Greece, with Lloyds Banking Group 1.485p lower at 29.6p, Barclays down 9.55p at 193.25p and Royal Bank of Scotland off 0.96p at 22p.

Other financial businesses are under pressure, with Man down 4.9p at 83p as investors continue to worry about the hedge fund group’s growth prospects.

Mining shares are also lower, after China’s move to cut its reserve requirement ratio – the amount of cash banks are required to hold as reserves – renewed worries about a slowdown in the country’s economy. Xstrata is down 38.5p at 1013.5p while Kazakhmys has fallen 28p to 736p.

Overall the FTSE 100 has fallen 103.11 points to 5472.41, a 1.8% decline which puts it on course for its lowest close since 22 December.

Only three companies are in positive territory, and two of them are in the traditional haven of the utilities sector. Severn Trent is up 4p at £16.97 while International Power – in the process of being taken over by majority owner GDF Suez – has added 0.6p to 419.6p. Meanwhile BSkyB is 0.5p better at 694p after giving an update on its share buyback programme

Among the mid-caps Invensys has jumped 9.7p to 212.2p as weekend reports rekindled recent talk of a possible bid for the engineering group, with Siemens, ABB, General Electric and China’s CSR all mentioned as potential predators.

Rank has risen 4.3p to 121p after it confirmed it was buying 23 UK casinos from Gala Coral for £205m in cash. Jeffrey Harwood at Oriel Securities issued a buy note, saying:

This is a sensible strategic deal for Rank. The transaction should be well received by the market; the shares look attractive on a single digit PE following the deal, although there are liquidity issues relating to the 74% interest of Guoco.

Elsewhere Plus Markets – home to the shares of Arsenal Football Club, Adnams and Shepherd Neame – has plunged 80% to just 0.22p after it ended a formal sale process with no satisfactory offers received. It now intends to close the business, winding down its operations over the next six months:

This will include working to ensure that companies traded on the Plus-quoted market are able to find suitable alternative arrangements for the trading of their shares.

Slowdown in April and May as weather adds to worries about consumer spending

Wickes-owner Travis Perkins has lost nearly 4% after it blamed wet weather for a weaker performance in April and the early May.

The builders merchant group, which also trades as City Plumbing and BSS, said revenues for the four months to the end of April were up 4.4%, but it saw a slowdown in growth in recent weeks:

After a good first quarter, record levels of rainfall contributed to a weaker performance in April and the early part of May, where activity levels at sites continue to be impacted by the very wet weather.

Travis said its outlook for the year remained unchanged but its shares are down 39p at 953p, and Peel Hunt’s Andrew Nussey said:

A highly uncertain consumer environment and hesitancy around capital spending creates earnings risk. While the shares offer good long term value, we sense there may well be better buying opportunities.

Analysts at Liberum Capital said the trading statement was “lacklustre.” Liberum’s Simon Irwin said Wickes should be less affected by the weather than B&Q owner Kingfisher, down 5.6p at 284.2p:

The next few weeks will be critical. The industry needs some good weather ahead of the Jubilee weekend to get seasonal out the door before they have to start discounting. [Kingfisher's] underlying story is still very strong but near term newsflow is unlikely to be helpful.

The Jamie Dimon apology tour is likely to continue on Tuesday as the CEO and chairman of the nation’s largest bank goes before shareholders at JPMorgan’s annual meeting.

Senior citizens may represent one of the smallest segments of Facebook’s 900 million users, but at least one group is eager to invest in this week’s IPO.