More than 1 billion people a day used Facebook in September
Facebook made the announcement during its third quarter earnings report, where it revealed that "DAUs (daily active users) were 1.01 billion on average for September 2015, an increase of 17% year-over-year."
Mobile accounted for a large chunk of that traffic, with 894 million DAUs on average coming from mobile users during September. That's a 27% year-over-year increase.
Beyond just the blockbuster month of September, Facebook reported 1.55 billion MAUs (monthly active users) as of September 30th, 2015. That's an increase of 14% year-over-year. Again, mobile made up for most of that traffic, with 1.39 billion MAUs, a 23% year-over-year increase.
Facebook stock was up nearly 5% on the news, but has settled to around 3%.