Updated: 11 p.m. ET

Social-networking site Facebook filed for its long-awaited initial public offering today.

The company said it wants to raise $5 billion -- and probably more -- in common shares in the offering.  The offering statement confirms that CEO Mark Zuckerberg, who turns 28 in May, is one of the nation's richest people already. His 28% stake in the company was valued at $15.9 billion at the end of 2011. If Facebook generates a valuation of $100 billion, the value of his holdings could jump to $28 billion.

Facebook, incorporated in 2004, had $3.7 billion in revenue in 2011 and $1 billion in net income. It says it has 845 million active users, who upload 250 million photographs a day and log 2.7 billion likes and dislikes every day. The users have 100 billion friendships.

Facebook's IPO is the most eagerly awaited since Google (GOOG) went public in a $1.67 billion IPO in 2004. The interest in the IPO was so great that it crashed the Securities and Exchange Commission's website late today.

Eighty-five percent of Facebook's revenue in 2011 came from advertising. That's down from 98% in 2009 and 95% in 2010. The rest of the revenue comes from payments derived from virtual goods used in social games.

Article continues below.The company's 2011 revenue was an increase of 88% over 2010's revenue of $1.97 billion. 2011's $1 billion in net income was a 65% increase from 2010's $606 million. The 2010 profit was up 164.6% from 2009.

About 44.3% of Facebook's revenue in 2011 camefrom outside the United States, up from 33% in 2009 and 38% in 2011.

Advertising accounted for about $3.15 billion of the company's ad revenue. Ads delivered grew 42% in 2011 over 2010. In addition, revenue per ad increased about 18%.

Fees generated by game develper Zynga (ZYNG) were responsible for about 11% of Facebook's revenue.

It gets a growing portion of its traffic from mobile devices. That business does not as yet generate much revenue. A challenge, the form S-1 statement says, is to find ways to generate revenue from the mobile traffic.

Facebook was started by Zuckerberg and a number of fellow Harvard students.

After Zuckerberg graduated, he started to build the operation into a for-profit venture. He was staked in part by his father, who was later awarded 2 million shares for his help.

in a letter from Zuckerberg that was part of today's filing, he insisted the profit was not the driving force. Facebook was "built to accomplish a social mission -- to make the world more open and connected."

Facebook has offices or data centers in more than 20 countries. It operates in Europe, Latin America and parts of Asia -- but not China.

Its competitors include Google, Twitter and Microsoft (MSFT), which already is an investor in the company. (Microsoft is the publisher of MSN Money.) 

Zuckerberg will still control the company
The offering will be Class A common shares, which come with 1 vote per share. The company's Class B shares get 10 votes each. Zuckerberg owns about 28% of the Class B shares and has effective control of the company, the statement says.

The offering statement filed with the SEC does not specify the number of shares to be offered or the price. The $5 billion amount is a placeholder used to calculate fees and may change.

But the number is, in fact, smaller than the $10 billion that was expected as late as last week.

The smaller deal size reflects a decision to start with a conservative base and gauge demand for the shares before deciding whether to increase the size of the offering and by how much, International Financing Review said Wednesday.

The filing timetable appears to establish a framework for Facebook to finalize the IPO process by May, pending a smooth registration process with the SEC. One reason to get the offering done by May, according to CNBC's Julia Boorstin: It lets insiders, normally not allowed to sell shares before six months, sell by the end of the year, before capital gains rates rise.

The networking site has opted to hire five lead investment banks, known as bookrunners, to handle the offering, featuring Morgan Stanley in the coveted lead role.

Goldman Sachs, Bank of America Merrill Lynch, Barclays Capital and JPMorgan and Allen & Co., the boutique investment bank that specializes in media deals, round out the initial list of bookrunners on the deal. IFR said the could also grow.

Investment banks commit to buy the shares and market them to prospective investors.

Recent trading in Facebook stock on private exchanges has pointed to an $80 billion-plus valuation, IFR said. The value of all class B shares on Dec. 31 was about $52.3 billion.

Facebook’s biggest outside stakeholder is venture firm Accel Partners, which first led a $12.7 million investment in 2005. Other investors include Microsoft and PayPal co-founder Peter Thiel as well as Greylock Partners.

As the site’s popularity grew, banks, hedge funds and mutual fund companies started buying stock. In January 2011, Facebook said it raised $1.5 billion in a financing round led by Goldman Sachs that valued the company at $50 billion.

Goldman Sachs, funds managed by the firm, and Digital Sky Technologies bought $500 million of stock, while Goldman Sachs offered $1 billion of shares to non-U.S. clients.

More about Facebook on MSN Money:

 

Largest IPO ever? Not nearly

 

Social-networking IPOs have been weak so far

 

To teens, Facebook is already over

 

Facebook's intriguing 'status update'