Facebook, which has filed the prospectus for its initial public offering seeking to raise $5 billion in initial funding, is yet to set its price range for the IPO but buying and selling of its stocks are already happening.

According to U.S. Securities and Exchange Commission rules, it is possible for insiders and investors with $1 million of net worth and a salary of more than $200,000 can qualify to buy stock on private marketplaces. Also in an auction last week on SharesPost, Facebook stock traded for $42, valuing the company at $98 billion.

For instance LinkedIn Corp, two months before the IPO, was valued at $35 a share in private trading in March 2011. Its IPO priced in May was at $45, giving it a valuation of $4.25 billion. Shares more than doubled to close at $94.25 on the first day of trading.

It is expected that demand for the IPO will push the stock even higher when Facebook, which reported in the filing $1 billion in profit on $3.7 billion in revenue last year, goes public.

Facebook first turned a profit in 2009, when it earned $229 million on $777 million in sales, according to the filing. At the end of 2011, Facebook had $3.9 billion in cash and marketable securities, up from $1.8 billion at the end of 2010.

In its IPO filing, Facebook revealed that it now has 845 million users, nearly half the world's Internet users.

In addition, the S-1 filing revealed how dominant founder and CEO Mark Zuckerberg's control of the company is with Facebook's structure of two classes of stock ownership and a highly unusual arrangement that gives Zuckerberg 57 percent of the voting power of Facebook stock.

The Facebook founder owns 533,801,850 shares of stock. Based on the company's last determination that those shares were valued at $29.73, his stake in the company would be worth more than $15.8 billion. He also has options to buy 120 million more shares.

Facebook has seen its user base grow phenomenally over time. Now it has to be seen how its share prices are going to grow with the advent of IPO.