Facebook (Nasdaq: FB), the No. 1 social network, announced it would increase the number of shares in its initial public offering, price them higher and value the company at as much as $104 billion. REUTERS

Facebook's record initial public offering is already oversubscribed, a source familiar with the share listing said on Thursday night, days after the world's largest social network embarked on a cross-country roadshow to drum up investor enthusiasm.

Despite concerns about slowing growth, a lofty valuation, and signs that the company is having trouble ramping up revenue from mobile advertising, institutional investors have so far indicated that there is more demand for shares than Facebook has available, the source told Reuters.

Analysts say the company, which seeks to raise about $10.6 billion by selling more than 337 million shares at $28 to $35 apiece, may raise that price range if demand turns out to be healthy enough.

One large institutional investor put in a major order for shares on Wednesday and was calling around syndicate desks trying to acquire more, a second source familiar with the IPO's progress told Reuters, declining to be identified because the details are not public.

Facebook declined to comment.

A Bloomberg Global Poll of 1,253 investors, analysts and traders who are Bloomberg subscribers, meanwhile, found that 79 percent believe that Facebook is overvalued at $96 billion.

Facebook is vulnerable to start-ups that may offer new, competing social media sites, Bob Rich, director of investments at Oppenheimer & Co., told Bloomberg. At the high end of a projected price range of $28 to $35 a share, Facebook would be valued at 99 times its earnings, a higher multiple than 99 percent of companies in the Standard & Poor's 500 Index.

This stock is going to come out, it's going to go to the moon, and then it's going to burn a lot of people, said Rich, one of the surveyed investors. The valuation is asinine, and I would not put my clients' money near it.

Facebook is seeking a valuation at 24 times revenue, compared to five times for Google, according to data compiled by Bloomberg.

Only 7 percent of those surveyed in the poll said Facebook was properly valued, while 3 percent said it was undervalued. Among respondents to the May 8 poll, 11 percent said they have no idea how Facebook should be valued.

The company that began in Mark Zuckerberg's Harvard dorm room project is expected to begin trading on May 18 after an IPO that dwarfs the coming-out parties of other tech powerhouses.

With 900 million users, it is challenging established Web businesses such as Google and Yahoo for consumers' online time and advertising dollars.

But in longer term, analysts say Facebook needs to develop a way to earn money from the increasing number of users who access the social network on mobile devices such as smartphones.

Facebook, which makes most of its money from advertising, began offering limited ads on the mobile version of its service only recently.