More than 1,000 people are now trading shares of Facebook on private markets, well above the 50 to 100 that most companies have ahead of their initial public offering.

Sam Hamadeh, head of research firm PrivCo., who made the current shareholder estimates for Bloomberg News, said that has pushed Facebook's valuation over $100 billion and could limit the returns the company's first public investors will see if they buy shares soon after the company goes public.

On private markets, Facebook was trading as high as $44 per share this month. That would give the company a valuation of $103 billion. Kevin Landis, portfolio manager for the Firsthand Technology Value Fund in San Jose, Calif., told Bloomberg that's up from October, when his fund purchased shares for prices between $30 and $31.

"Facebook is a blue-chip stock and it's not even public yet," said Landis, who still hopes to add Facebook shares to his fund.

Facebook, which is not commenting as a result of its mandated quiet period ahead of the IPO, has not set price ranges for its offering. Insiders have said founder Mark Zukerberg has considered valuations as high as $100 billion.

Barry Ritholtz, CEO of FusionIQ, an equities research firm, told Bloomberg the heavy activity on the private markets could make the IPO more like a secondary stock offering.

"The people buying now at the IPO price are presuming there's lots of upside - I'm skeptical," said Ritholtz. "There's a lot of smart money agitating for the highest possible valuation, and they don't necessarily have the investing public's best interest at heart."