Fourteen analysts surveyed by Zacks Investment Research expected $13.4 billion.
Although Facebook shares were in a slump after the Cambridge Analytica scandal broke earlier this year, the stock had risen sharply and hit record levels this month.
Zuckerberg's paper losses come after Facebook revealed mixed earnings and slowing growth during the second quarter of 2018.
What is your opinion over Facebook's Q2 2018 earnings? It was the first full financial report since Facebook became embroiled in the Cambridge Analytica scandal in March.
Expenses are expected to grow 50 percent to 60 percent compared with past year as the company invests in security, marketing and content acquisition, he said.
Facebook's first financial stumble in three years followed a quarter in which data-privacy issues came under harsh scrutiny, with chief executive officer Mark Zuckerberg testifying before US Congress for hours on the company's missteps. And the company was bombarded by public criticism over its content policies, especially in countries such as Myanmar and Sri Lanka where misinformation has led to violence.
"So far, there has been no evidence that shows that controversies, such as the spread of fake news, Russian interference in the US elections, and the Cambridge Analytica scandal, have prompted advertisers to divert ad dollars", says Haris Anwar, senior analyst at Investing.com.
All of those problems are hitting amid a harsh truth for the company: Facebook, the social network with 2.23 billion active monthly users, can't grow forever.
Net income attributable to Facebook shareholders rose to $5.11 billion, or $1.74 per share, in the second quarter ended June 30 from $3.89 billion, or $1.32 per share, a year earlier. The company's user base was unchanged in its biggest market, the USA and Canada, at 185 million daily users, while declining in Europe to 279 million daily users. Additionally, its daily active users-to-monthly active users ratio was held at 66 percent, showing that users were still hooked on using the social network. In terms of revenue, the tech giant earned $13.23 billion but missed Thomson Reuters' estimates of $13.36 billion. Analysts projected $13.3 billion.
The company remains in a dominant position in mobile advertising alongside Alphabet Inc's Google.
Gene Munster, a venture capitalist at Loup Ventures, said in an email that Facebook is "entering a new period" where declining user growth will translate to slower revenue growth.
If the share drop holds on Thursday, it would be Facebook's largest single-day decline, topping a 12 percent decrease in July 2012. In North America, an effort to get all political advertisers to verify their identities may have halted some purchases as the company worked through its broad definition of what's considered "political".
Instagram has grown to 1 billion monthly users from 600 million in late 2016, while Facebook's two messaging apps, Messenger and WhatsApp have each reported well over 1 billion monthly users. Given all the questions about the misuse of the platform, "to explain that there are a couple million people who chose not to continue using Facebook is unsurprising", said Brian Wieser, an analyst at Pivotal Research.
One app that received a special shout-out from Zuckerberg on Wednesday's earnings call: Instagram.
Facebook forecast similar increases for the second half of the year, also citing spending on video content and marketing.
Zuckerberg said Wednesday that he was hopeful Facebook would be able to limit disinformation and fake accounts, and that the company was able to do so in elections this year in France, Mexico and Germany.
Facebook shares have increased 23 percent since the beginning of the year, while the Standard & Poor's 500 index has increased 6.5 percent.
The revenue guidance from the company was "unprecedented", said Gene Munster, an analyst at Loup Ventures, in a note to investors.