Can Twitter keep up the solid growth in user base?

Twitter‘s stock jumped nearly 30 percent in after-hours trading on Tuesday following the release of its quarterly earnings, as a solid growth in active users soothed concerns about the future of the microblogging site, but some analysts remain skeptical.

As if to downplay the positive impact of the World Cup event on Twitter’s second quarter results, CEO Dick Costolo stressed in a CNBC interview that the sporting event – which started on June 12 and went through July 13 – was not behind the pickup in monthly active users (MAUs) last quarter.

But Eric Bleeker, analyst at the Motley Fool says his comments should be taken with some caution, saying the once-in-four-years sporting event evidently helped Twitter, raising concerns about whether that expanding pace in user base can be sustained in the absence of global events.

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Twitter picked up 16 million MAUs to bring its total to 271 million – topping analyst expectations for 267 million – the biggest period of user growth since the first quarter of 2013. Three million new users were added in the U.S. – its most lucrative market – while it added 13 million internationally.

“I think investors would be wise to take what Twitter said about the World Cup not affecting monthly users with a grain of salt, and watch next quarter to see if this growth is sustainable,” Bleeker told CNBC.

“While reviewing their earnings call I counted 20 mentions of World Cup, and five analyst questions were centered on it. Clearly, it had a big impact,” he added.

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During the quarter, the social networking giant reported net revenue of $312 million, up 124 percent year-on-year, with strong performance in its mobile advertising space. But the company remains unprofitable, posting a net loss of $145 million.

Charles Sizemore, chief investment officer at Sizemore Capital Management has doubts over whether the company will be able to maintain the pace of its bumper revenue growth, noting that user engagement could decline after the World Cup.

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“With Twitter users more engaged during the World Cup, my assumption is that advertisers were willing to pay more. That’s great for this past quarter, but it isn’t something we should expect to see repeated,” he said.

Emmanuel Dunand | AFP | Getty Images A banner with the logo of Twitter is set on the front of the New York Stock Exchange.

Emmanuel Dunand | AFP | Getty Images
A banner with the logo of Twitter is set on the front of the New York Stock Exchange.

But not everyone believed World Cup had as big an impact on Twitter.

“They would have beaten expectations handedly anyhow. I don’t think this is a one quarter phenomenon. Twitter is really just getting started on the monetization side,” said Richard Fetyko, senior vice president, equity research, Internet Tech and Media Department at ABR Investment Strategy, citing rival Facebook’s success in monetizing its user base.

Twitter’s average revenue per user was $1.15, versus $0.98 in the first quarter and $1.01 in the fourth quarter of 2013. This compares with Facebook’s average revenue per user of $2.24.

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“Twitter is halfway where Facebook is today and Facebook is still going to still double or triple its monetization per user over the next three years,” Fetyko said.

Fetyko has a bullish view on Twitter’s stock, forecasting it will reach over $60 in the next 12 months – marking 55 percent upside.