Facebook earnings preview: Mobile and growth in focus

When Facebook reports its second-quarter earnings after the bell Wednesday, the big question will be how well it's growing its mobile revenue—an issue that dragged its post-IPO performance.

Analysts' consensus is that 33 percent of Facebook's total ad revenue will come from mobile devices. Other key growth drivers include international advertising growth and higher-priced ads in users' news feed rather than on the side of the page. And growth of Facebook's gifts business and popular social games are expected to drive the "payments and other revenue" segment 8 percent higher, according to analyst estimates.

Facebook's revenue is expected to grow 37 percent, to $1.62 billion, while earnings per share is forecast to grow 14 percent, to 14 cents, up from 12 cents a year earlier.

Looking forward to the rest of the year, what investors want to hear is whether users continue to be engaged—and how well they're responding to mobile ads.

(Read more: Earnings deluge begins today—here's what to expect)

On the earnings call, we can expect plenty of questions about how well Facebook's new ad formats are working, and how compelling users find new products such as Graph Search and Instagram video. And Facebook is likely to address persistent concerns about whether it is losing ground to newer services such as SnapChat.

Morgan Stanley's Doug Anmuth will be listening on the call for additional data or commentary on user engagement—beyond daily and monthly active users—in light of the growing popularity of Twitter, WhatsApp and Snapchat.

"We continue to believe that competing services are having only a modest impact on Facebook ... and higher mobile usage is driving continued engagement share gains," Anmuth wrote in a research note. He also will be looking for insight into ad trends in the second half, expecting growth driven by improved and streamlined ad options.

RBC Capital Markets analyst Mark Mahaney, who has an outperform rating on the stock, says Facebook appears to have "addressed the biggest issues from its IPO days—Mobile monetization and Zynga revenue dependency."

While concerns about "decreasing youth engagement" may be justified, the company has "demonstrated an impressive ramp in mobile revenue over the last year. Mobile is now largely driving overall advertising revenue growth," Mahaney wrote in a research note. "And we think it can reach over 1/3 of Facebook's total revenue in Q2: 13."

The question is what that growth will mean for margins.

(Read more: Here come the earnings—more surprises ahead?)

According to Mahaney, that Facebook reiterated its guidance for a 50 percent increase in operating expenses is a good thing. "We view this move as a positive demonstration of a commitment to maintaining the velocity of product improvements," he wrote.

Lazard's William Bird, with a neutral rating on the stock, is concerned about the potential for slowing growth, given "tougher mobile comps, flattish desktop trends and likely slow commercialization on new product initiatives." Bird warns that Facebook's business model is still in transition.

Lazard collaborated with Clear Voice Research to survey more than 1,000 adults on their social media behavior and found that those planning to spend less time on Facebook outnumbered those planning to spend more time by a factor of 2.2 times. The respondents said that increased advertising has a negative effect on their experience.

We'll see if Facebook's results bear out those comments.

—By CNBC's Julia Boorstin. Follow her on Twitter: @JBoorstin