What happened

Shares of Facebook (NASDAQ:FB) have dropped today, down by 6% as of 12:20 p.m. EST, after the company reported its fourth-quarter earnings results. Though the social networking titan beat expectations, investors are concerned about slowing growth rates.

So what

Revenue in the fourth quarter increased 25% to $21.1 billion, which was ahead of the $20.9 billion in sales that analysts were modeling for. That all translated into net income of $7.3 billion, or $2.56 per share. Investors were expecting just $2.52 per share in profits. Family monthly active people (MAP) -- folks that use one of the tech giant's core services each month -- grew 9% to 2.89 billion.

Mark Zuckerberg on stage

Facebook CEO Mark Zuckerberg. Image source: Facebook.

"We had a good quarter and a strong end to the year as our community and business continue to grow," CEO Mark Zuckerberg said in a statement. "We remain focused on building services that help people stay connected to those they care about."

Now what

Investors were concerned about decelerating growth, as that top-line growth rate was the lowest that Facebook has ever posted. The company's outlook also braced shareholders for continued deceleration, with CFO Dave Wehner saying that revenue in the first quarter should "decelerate by a low to mid-single digit percentage point as compared to our Q4 growth rate." The finance exec attributed the deceleration to a maturing business combined with headwinds related to the advertising market as global privacy regulations intensify.

Facebook reaffirmed its 2020 outlook for total expenses ($54 billion to $59 billion) and capital expenditures ($17 billion to $19 billion).