Facebook Inc will increase the size of its initial public offering by 25 percent, a source familiar with the matter said, and could raise as much as $16 billion as strong investor demand for a share of the No.1 social network trumps debate about the company's long-term potential to make money, Reuters reported.

Those concerns over revenue growth were underscored earlier on Tuesday, when General Motors said it planned to pull out of advertising on Facebook.

Facebook, founded eight years ago by Mark Zuckerberg in a Harvard dorm room, will add about 85 million shares to its IPO, floating about 422 million shares in an offering expected on Friday, the source told Reuters, declining to be identified because the information was confidential.

The expanded size, coupled with Facebook's recently announced plans to raise the IPO price range, would make Facebook the third-largest initial share sale in U.S. history after Visa Inc and GM. Facebook declined to comment on the increased IPO size.

Before the IPO size was increased, Facebook would have raised about $12.1 billion based on the midpoint price of $36 and the 337.4 million shares on offer originally.

At this midpoint, Facebook would be valued at roughly 27 times its 2011 revenue, or 99 times earnings. Google went public at a valuation of $23 billion, or 16 times its trailing revenue and 218 times earnings. Apple Inc went public in 1980 at a valuation of 25 times its revenue and 102 times earnings.