Doubts over the valuations of social networking websites were assuaged yesterday after Sir Li Ka-shing, one of Asia’s most successful investors, doubled his stake in Facebook, underlining the site’s implied price tag of $15 billion (£7.5 billion).

The Hong Kong billionaire’s investment was made through the Li Ka-shing Foundation, which spent $60 million to increase his stake to 0.8 per cent of the company. That matches the $60 million that he invested last year and is valued on the same terms as the $240 million stake that Microsoft took in October.

The cost of the holdings that both took in Facebook represents a value for the whole networking site group of $15 billion.

Wall Street is nervous that social networking sites are a fad and that they have been unable to translate their popularity into online advertising revenues.

In previous rounds dating back to 2004, Facebook has taken about $40.7 million from venture capital investors, including Peter Thiel, PayPal’s co-founder and former chief executive, Accel Partners, Greylock Partners and Meritech Capital.

Mark Zuckerberg, the founder of Facebook, opened the site to users beyond its original student base only 18 months ago. Its user base has since ballooned to more than 47 million people. Facebook competes with the larger MySpace, which has 100 million users. It is thought that Mr Zuckerberg intends to prepare Facebook for a float.

Rupert Murdoch, the chairman and chief executive of News Corporation, parent company of The Times and owner of MySpace, has ruled out buying Facebook, saying that it was overvalued. News Corp bought MySpace for $580 million in 2005.

In October, Facebook opened the door to outside developers for the first time, attracting 4,000 applications. Facebook will allow these developers to profit from their applications, which include games, widgets and other more practical tools.

This year, AOL unveiled a deal to buy Bebo, the social networking site, for $850 million, fuelling speculation about valuations of such sites.

Hutchison Whampoa, Sir Li Ka-shing’s conglomerate, is focused on ports and telecoms ventures.

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