On the advertising revenue, Facebook also beat analysts' average expectation of $5.15 billion — according to StreetAccount — with a blow-out $5.64 billion in the quarter. Mobile advertising revenue, meanwhile, came in at $4.51 billion, Facebook said, against expectations of $4.09 billion.
Mobile advertising revenue represented about 80 percent of all ad revenue, the company said, compared to about 69 percent in the year-ago period. Ad impressions on mobile, meanwhile, increased 29 percent on a year-over-year basis, Facebook CFO David Wehner said, adding that 2015's final quarter was the first since Q3 2013 in which total ad impressions increased against the year-ago period.
There are now more than 2.5 million active advertisers working with Facebook, Zuckerberg said on the call.
For the fourth quarter, Facebook saw average revenue per user (ARPU) of about $3.73, while Wall Street had only expected $3.43, according to StreetAccount.
"The revenue per user is an important number, but I always kind of look at usage more than users," said Martin Pyykkonen, senior research analyst at Rosenblatt Securities. "Facebook is getting to a deceleration in that, but the average revenue was still very strong."
Despite the quarter's strong revenue figures, Wehner cited the strengthening U.S. dollar's "unfavorable impact" on the company's financials. Had exchange rates remained constant with the year-ago period's levels, total revenue would have been about $320 million higher, Wehner said on the call.
That strong dollar will continue to affect comparisons, he predicted, saying that Facebook expects "to continue to face foreign exchange headwinds, especially early in the year, as we will be lapping periods where the dollar was relatively weaker than it is today."
More broadly, Wehner predicted that the company will also face "tougher" comparisons throughout 2016 given the "remarkably strong advertising performance" last year.
Looking at the global macroeconomic environment — which has recently given many companies trouble — Wehner said Facebook did not see anything in its fourth quarter that indicated "broad-based macro weakness" beyond currency effects.