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Facebook stock declined in after-hours trading Tuesday after a quarterly earnings beat and a disappointing outlook, making it a "sell," Brian Kelly of Brian Kelly Capital said.

Earnings clocked in at 43 cents per share on $3.20 billion in revenue, beating Wall Street estimates of 40 cents and $3.12 billion in revenue. Facebook shares, which closed up 0.61 percent at $80.77, sold off 10 percent after the market close.

On CNBC's "Fast Money," Kelly said that he would look elsewhere in the social media space.

Source: Facebook

"So, Twitter reminds me of Facebook two years ago, where everybody hated Mark Zuckerberg, nobody thought they could monetize mobile, everything was going wrong with Facebook and today we're all cheering it," he said. "So, what would B.K. do? B.K. would take his profits in Facebook and buy Twitter instead."

Kelly noted Facebook stock had run up 14 percent in the past 10 days.

Read MoreFacebook shares drop on guidance, costs

"It's not that I hate Facebook," he added. "I'm just saying given the choice, if I have two stocks, I think there is so much more upside in Twitter—'cause all they have to do is one thing right—than there is in Facebook."

Kelly, who doesn't own shares of either social media name, said that he might buy Twitter stock.

Private Advisor Group's Guy Adami said Facebook's monthly active users for the quarter, which were up 14 percent year over year to 1.35 billion, failed to rally the stock because they were in line with analysts' expectations.

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"That's the only thing I can think of," he said. "I think it's a fantastic quarter."

Triogem Asset Management's Tim Seymour said that Facebook had raised the bar.

"These guys are doing everything they're supposed to," he said. "Google and Facebook own it, and it's getting to a place where I think it's going to be tough to compete."

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