Sponsored Stories appear in the user's news feed. If one or more of a user's friends has "liked" a particular brand, the user sees an item about that action in his news feed. The ads receive more prominent positioning in the news feed than other content, advertisers and analysts said.

Third-party studies have also indicated that the mobile ads have been successful. A report released on Tuesday by AdParlor, a firm that runs Facebook marketing campaigns, said Sponsored Stories actually perform better on mobile than they do on the desktop.

Users were 11 times more likely to click on a Sponsored Story on their mobile device than one on their desktop, the study found. However, those who clicked were 20 percent less likely to "like" the promoted brand. Mobile sponsored stories are still a buyer's market, with advertisers paying less per click than on desktop, according to the study.

But analysts suggested Facebook has more work to do to tackle its mobile problem.

Facebook won't be able to bet on Sponsored Stories as its main mobile advertising offering for long, said analysts interviewed before the company's earnings were released. With the mobile advertising market likely poised to enter a period of dramatic innovation, the company will have to invest in improvements to its mobile platform that keep users engaged and enable more sophisticated forms of marketing, the analysts said.