Facebook reported a 9 percent fall in quarterly profit as it spent heavily to boost mobile revenue and develop products such as messaging service WhatsApp, photo-sharing app Instagram and virtual reality headset maker Oculus Rift.
Shares of the social network fell 4.2 percent to $92.90 in after-hours trading on Wednesday.
Facebook's total costs and expenses jumped 82 percent to $2.77 billion in the three months ended June 30.
The company had warned that 2015 would be a year of heavy investment, but analysts have said these investments are likely to translate into significant revenue streams in coming years.
Mobile ads accounted for 76 percent of Facebook's advertising revenue of $3.83 billion in the second quarter, compared with 62 percent in the same quarter last year.
Video ads, which Facebook began offering last year, is the fastest growing category of Internet advertising. The business is currently dominated by Google, owner of YouTube, but analysts say Facebook is catching up fast.
Facebook said it had 1.49 billion monthly active users as of June 30, up 13 percent from a year earlier. Of these, 1.31 billion accessed the service through mobile devices, a rise of 23 percent.