Facebook has hit a new milestone: the site now has 1 billion users.

The company’s chief executive Mark Zuckerberg made the announcement Thursday morning, in a brief statement on its Web site.

“If you’re reading this: thank you for giving me and my little team the honor of serving you,” Zuckerberg wrote. “Helping a billion people connect is amazing, humbling and by far the thing I am most proud of in my life.”

Facebook certainly has been busy lately. The company is launching new initiatives as it searches for ways to boost revenue inside and outside of the confines of its social network.

The company is now seeing its fastest growth in Brazil, India, Indonesia, Mexico and the United States. Many users are also coming to Facebook through its mobile site, which has an average of 600 million users. The average age of a Facebook user is 22.

Facebook also touted its strength as a multimedia hub. At last count, more than 219 billion photos have been uploaded to the site, excluding those that have been deleted, and users have listened to 62.6 million songs at least 22 billion times.

That means Facebook users have spent a cumulative 210,000 years simply listening to music, the company said.

And how goes the site’s primary goal of “connecting the world”?

All told, the site has logged 140.3 billion friend connections, 17 billion of which have been tagged with users’ locations. And users have reached for the “Like” button on Facebook and other sites more than 1.13 trillion times since the widget went live in February 2009.

Facebook hit its last major milestone — 500 million users — in July 2010. The social networking site officially hit the 1 billion user mark on Sept. 14 at 12:45 p.m. Pacific time, according to a fact sheet posted by the company. The company did not explain why it delayed the announcement.

In an interview with Bloomberg, Zuckerberg said that the company’s employees watched the user count and “everyone came together and counted down” when it became clear that Facebook would hit one billion users.

He also touched, briefly, on the company’s poor stock performance since its May debut on the public market. After debuting at $38 a share, Facebook’s stock has fallen as low as about $17. It closed Wednesday at about $21 a share.

“The performance has obviously been disappointing,” Zuckerberg told Bloomberg reporters. “ And I think the only thing we can really do is focus on making the company worth as much as possible over the long term.”

As the company pursues its next billion users, Zuckerberg said it will make a “big push in commerce” and focus on building it mobile userbase.

Mobile devices, he said, can be a much better place to deliver advertising because they’re more integrated into the users’ content than when the ads are viewed on a personal computer.

“The advertising and monetizing has to be integrated in, whereas on desktop we kind of reached this equilibrium where there’s the content and then the ads off to the side of it,” Zuckerberg said. “So I’m really optimistic about that.”

(Washington Post Co. Chairman and Chief Executive Don Graham is a member of Facebook’s board of directors.)

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