Pro on Twitter earnings: Buy Facebook instead

Wall Street will turn its attention on Tuesday to Twitter, the micro-blogging website, which is scheduled to report its second quarterly earnings results after the closing bell.

It seems few, if any, investors are willing to bet on the social media stock ahead of earnings, too. After all, Twitter runs the risk of being overshadowed by rival Facebook, which beat earnings expectations last week thanks to higher advertising revenues.

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To Rich Greenfield, a media and technology analyst at BTIG, investors should "continue to exercise caution" on Twitter, especially ahead of its earnings report. The company simply lacks the reach Facebook has, in terms of both total users and engagement, he said.

"The users are still far smaller and growing pretty slowly relative to what we're seeing at Facebook, and I think that's the real challenge is how big can Twitter be?" Greenfield said on "Squawk on the Street." "The problem is, how do they convince your mom, how do they convince your friends, [that] they have to be on Twitter the way they're on Instagram or on Facebook?"

Last week, CNBC's Jim Cramer expressed similar concerns about buying Twitter ahead of earnings.

"I think this one could be very problematic because Facebook delivered such a great number and Twitter could suffer by comparison," Cramer said on "." "Frankly, I wouldn't recommend buying Twitter until it drops back to $29, a huge decline from these levels. Until then, just stick with Facebook."

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Greenfield also recommends investors opt for Facebook shares over Twitter's stock. He pointed to Facebook's "staggering" ad revenue growth, noting the world's No. 1 social network boasted a bigger worldwide ad revenue for the past quarter than Time Warner and Viacom combined.

—By CNBC's Drew Sandholm.