NEW YORK – Facebook's beleaguered stock has lost more than half of its value since its initial public offering three months ago.

Facebook Inc.'s stock slid 7 cents to $18.98 in morning trading Monday. Earlier, it hit $18.75, a new low. The social networking icon's much-anticipated IPO turned sour amid technical problems on the NASDAQ stock market and high expectations. The stock has not surpassed its $38 IPO price since its first trading day.

Investors are worried about Facebook's ability to grow revenue quickly, especially when it comes to garnering mobile advertising dollars as users flock to smartphones and tablet computers. There are also looming expirations of the IPO lockup periods. Lockups preventing many Facebook employees from selling stock expire this fall, potentially flooding the market with more shares.