Facebook warns advertising revenue growth will slow
Facebook has warned growth in advertising revenues will slow "meaningfully" in the next few months as it tries to avoid alienating users.
The social media giant's chief financial officer David Wehner said there was a limit on the number of ads it could put on people's timelines.
Shares fell 7% in after-hours trading.
The comments came as Facebook reported profits of $2.4bn (£1.9bn) between July and September, up 166% from the same period in 2015.
Most of Facebook's revenues came from adverts, of which mobile accounted for 84%.
Facebook founder Mark Zuckerberg described the results as "another good quarter".
Nearly 1.1 billion people now log onto Facebook on their mobiles every day, compared with 894 million a year ago.
But it has not been all plain sailing for the firm. In the past few months it hasapologised for unfairly removing certain content, and admitted itoverestimated how much video users have watched for the last two years.
Meanwhile Whatsapp, the messaging app Facebook bought for $19bn in early 2014,has been warned by European privacy watchdogs about sharing user data with its parent company.