Facebook Inc. FB +0.93% posted a quarterly loss Tuesday as costs mounted, but the social site also issued some encouraging data on its progress in making money from mobile phone use.

Shares of Facebook rose as much as 10% in after-hours trading as the company’s earnings and revenue were slightly ahead of Wall Street’s expectations. As of the close, the stock had fallen almost 50% from its initial public offering in May.

Overall, Facebook posted 32% revenue growth in the quarter compared with the period last year. That growth is flat with the prior period—its slowest rate in at least a year—and down from the 45% growth posted in the first quarter of this year.

But many investors appear to be focusing on where Facebook’s ad revenue is coming from: The company said that 14% of its advertising sales in the period came from mobile devices. That percentage amounts to roughly $150 million.

Facebook has been dogged by criticism of its ability to make revenue from the growing use of its site on mobile phones.

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