Facebook Inc. is already trading like a public company asinsiders and wealthy investors use private marketplaces to buy andsell stock in the social-networking company ahead of its initialoffering.

The shareholder base has grown to more than 1,000, compared withthe 50 to 100 investors most companies have when they go public,according to an estimate by Sam Hamadeh, head of research firmPrivCo. Private purchases pushed Facebook's valuation past $100billion this month, possibly limiting immediate gains for IPOinvestors, given that Facebook may seek a $75 billion to $100billion value.

“Facebook is a blue-chip stock and it's not even public yet,”said Kevin Landis, portfolio manager for the Firsthand TechnologyValue Fund in San Jose, California. Facebook jumped as high as $44this month in private trading, valuing the company at $103 billionand leaving it higher than when Landis bought stock at about $30 to$31 in October. He said he aims to add to his holdings.