Facebook's 900 million users helped the company generate just $1bn in profit last year, and there are concerns about its ability to increase profits in the future.
The flotation was disrupted on its first day of trading by technical glitches on the Nasdaq stock exchange. The share price has since slumped amid worries that the company was over-valued by advisers marketing the float.
Now, a group of investors has issued a class-action lawsuit alleging that Facebook revenues were revised down because of a surge in the number of people using mobile devices for apps and connection to websites.
The suit targets Facebook, its founder Mark Zuckerberg and the banks behind the flotation, including lead underwriter Morgan Stanley.
The share sale in New York raised $16bn for Facebook.