Facebook stock tumbles in second day of trading

The price leveled out by mid-morning and closed at $34.03.

The company, which Mark Zuckerberg founded in his Harvard University dorm in 2004, now has more than 900 million users worldwide, with about 188 million in the United States and Canada.

But investors might be worried about the company's ability to squeeze enough revenue out of its users to justify its valuation. Last year, the company's profits were $1 billion, which is small considering its massive user base.

The majority of Facebook’s revenue comes from advertising, but the company has acknowledged that it will need to find ways to better display ads to smartphone users. 

The level of detail Facebook collects on its users has also drawn criticism from some regulators and lawmakers. The company has acknowledged that new privacy regulations could hurt its business model.