It’s hard to find much that’s going to slow down Facebook Inc. — least of all in its second-quarter earnings announced today.

Thanks to continuing strong mobile ad sales, now 87 percent of revenue, the social network reported a second-quarter profit of $3.9 billion, or $1.32 cents a share. That was up 71 percent from a year ago.

Revenue jumped 45 percent, to $9.32 billion. Analysts had expected a profit of $1.12 a share on revenue of $9.17 billion, according to a poll by FactSet.

Initial confusion on the results resulted in as much as a 4 percent drop in shares in immediate after-hours trading, but investors quickly reversed course and shares rose about 1.5 percent. The stock had closed up a fraction in regular trading, to $165.61 a share. Facebook’s shares are up 40 percent on the year as its ad machine has rolled on unimpeded either by longstanding competition with Google Inc. or upstarts such as Snap Inc.

Not surprisingly for an app that already claims 2 billion users, Facebook said user growth continues to slow. The number of monthly active users rose 17 percent from a year ago. Daily users rose the same percentage, to 1.32 billion. Either way, the slowdown in user growth isn’t hitting the top or bottom lines.

Analysts have been confident about Facebook’s prospects as well, despite the company’s own warnings since last year that growth would slow as it eased off on increases in ad load on the core news feed. “The revenue growth in the quarter is all the more remarkable considering the concerns that came to light late last year around measurement issues, use of third party tools by large brands and broader concerns about the effectiveness of digital advertising among many large advertisers,” Pivotal Research Inc. analyst Brian Wieser said in a note to clients today.

Wieser is concerned longer-term by potential saturation of the digital ad market as Facebook and Google Inc. together account for most of the industry’s growth. But other analysts are more sanguine. “We continue to like FB based on its continued usage gains (driven by Instagram), advertiser growth (now over 5 million), emerging opportunities (video, messaging, network, search, AR/VR, etc.), and ability to execute,” Macquarie Capital analyst Ben Schachter wrote in a recent Internet stock report.

Higher costs remain a point of concern. Capital spending for all those data centers to run video hit $1.44 billion, up from $995 million a year ago. Beyond that, Facebook has had to take a much more active role in policing content.

This quarter, the company said it would hire 3,000 workers to help keep violent or offensive material off the site, after European policymakers threatened to punish Internet companies that enabled terrorists to use social and other services to plan and coordinate attacks. Overall, Facebook’s head count is up 43 percent from a year ago, to 20,658.

Still, those expense increases trail well behind revenue growth, thus that big uptick in profit. And Chief Financial Officer David Wehner said on the call that the company is narrowing and potentially lowering its expense growth range for the year from between 40 and 50 percent to 40 to 45 percent.

Investors are keen to get a better idea of how much Instagram is contributing. Facebook hasn’t disclosed that and probably won’t very soon. EMarketer has forecast that the photo-sharing app will gross $3.9 billion in worldwide ad revenue this year, more than double last year and about five times what Snapchat is expected to post.

A key question Facebook didn’t answer was whether the upside came from more of the same video ads or more engaging made-for-mobile video ads. “Mobile ads tend to command lower prices than desktop and video tends to command higher prices than display on any device, so to me the details would be more compelling than the aggregate results,” said Melissa Parrish, vice president and research director at Forrester Research Inc. “Are marketers buying fewer, higher-quality, higher-engagement, higher-cost ads? Or are they just buying more of what they’ve been buying?”

One indication came in the 24 percent increase in ad prices in the quarter, the company reported. That’s an indication that certain ads, at least, are commanding much higher prices thanks to the results advertisers are getting.

There could be more in the way of ad opportunities coming, but the impact could take awhile. On July 11, Facebook started showing ads on its Messenger app, which has some 1.2 billion users, and reports say it will be looking to offer some kind of advertising before long on WhatsApp, which has well over a billion monthly active users. In particular, Facebook said some 250 million people daily use Instagram Stories, the knockoff of Snapchat’s own Stories, and the same number use WhatsApp’s similar Status.

But although Chief Operating officer Sheryl Sandberg said both have big opportunities for brands to reach consumers, Chief Executive Mark Zuckerberg (pictured) repeatedly said Facebook would “make sure we get this right” before rolling out many ads on the messaging platforms. Video ads will be much bigger for Facebook over the next two to three years, he said.

Zuckerberg also gave a shout-out to artificial intelligence on the earnings call. He said it’s already improving existing services, such as flagging unsavory content. But he hopes AI in the future “will help you discover what’s going on out there beyond just what your friends are up to.”

Photo: Robert Hof