Facebook's monthly active users (MAUs) were 1.01 billion as of September 30, 2012, an increase of 26% year-over-year. Daily active users (DAUs) were 584 million on average for September 2012, an increase of 28% year-over-year. Meanwhile, mobile MAUs were 604 million as of September 30, 2012, an increase of 61% year-over-year.
"As proud as I am that a billion people use Facebook each month, I'm also really happy that over 600 million people now share and connect on Facebook every month using mobile devices," said Mark Zuckerberg, Facebook founder and CEO. "People who use our mobile products are more engaged, and we believe we can increase engagement even further as we continue to introduce new products and improve our platform. At the same time, we are deeply integrating monetization into our product teams in order to build a stronger, more valuable company."
http://investor.fb.com/releasedetail.cfm?ReleaseID=715607