Smile, you've just become Facebook millionaires!

Mark Zuckerberg rang the morning bell at 9:30 EST from Facebook headquarters in Menlo Park, California, to launch the second-largest IPO in U.S. history - and to instantly increase his personal wealth by as much as $20billion.

Workers at Facebook’s headquarters in California also celebrated ahead of yesterday’s mammoth $104billion flotation of shares in the social networking website in an unusual way.Millions of new investors will be wary come next week amid fears as the IPO failed to match expectations.

Some market experts blamed trading problems and an anxiety-filled half hour where traders were having problems placing and cancelling orders for Facebook stocks. To IPOdesktop's Francis Gaskins, it means mom-and-pop investors are becoming 'much more educated and careful' about not buying into hype.

The closing price means Facebook is now worth about $105billion, more than Amazon, McDonald’s, and storied Silicon Valley icons Hewlett-Packard and Cisco.

When trading began, shares were selling around 10 per cent higher than anticipated, around $42 per share, with 100million sold within the first five minutes.

By noon, trading had leveled out to the expected $38, and Facebook finished its first day on the market at a modest $38.23, only 23 cents higher than its initial estimated IPO.The offering values Facebook, whose 2011 revenue was $3.7billion, at as much as $104 billion. Google, whose revenue stood at $38billion last year, has a market capitalization of $207billion.

Inside Facebook