By Yasmeen Abutaleb and Devika Krishna Kumar (Reuters) - Twitter Inc reported quarterly revenue that fell short of Wall Street estimates and cut its full-year forecast because of weak demand for its new direct response advertising, sending shares down as much as 24 percent on Tuesday. User growth was off to a slow start in April, the company said, even though it hit its own target for the just-ended first quarter. Twitter forecast 2015 revenue of $2.17 billion to $2.27 billion, down from its earlier forecast of $2.3 billion to $2.35 billion. Analysts on average had been expecting $2.37 billion. Twitter said its new direct response ads, intended to encourage actions such as clicking on a link to an advertiser's website, did not produce the revenue expected. Advertisers limited their spending and the click rate on Twitter's ads fell, but the company expects improvement in the second half of 2015, Chief Financial Officer Anthony Noto said on a call with analysts. The company, which allows users to broadcast 140-character messages, said revenue rose to $436 million in the first quarter, from $250.5 million a year earlier. This was below the average analyst estimate of $456.8 million, according to Thomson Reuters I/B/E/S. (http://bit.ly/1GCvh0y) Concerns about Twitter were exacerbated when the results were leaked before the market closed. Market data firm Selerity tweeted the figures, saying it had found the release on Twitter's investor relations website. Twitter blamed the Nasdaq, which it said managed its investor relations website. "Everything looked weaker than expected," said Arvind Bhatia, a SterneAgee CRT analyst. "This sort of loss of momentum is probably going to cause a bigger outside reaction than in normal circumstances." The company's monthly active users rose 18 percent from the previous year to 302 million, in line with some analysts' expectations. Twitter's net loss widened to $162.4 million, or 25 cents per share, for the quarter, from $132.4 million, or 23 cents per share, a year earlier. Excluding items, the company earned 7 cents per share, above the 4 cents per share expected by analysts. Selerity's tweet about Twitter's earnings raised questions about the social media company's internal controls, said Brian Jacobsen, chief portfolio strategist at Wells Fargo Fund Management. Ahead of earnings on Tuesday, Twitter said it had acquired marketing technology company TellApart to ramp up its direct response advertising. Twitter shares closed down 18.2 percent at $42.27 on the New York Stock Exchange, and fell further to $41.89 after hours. (Reporting by Yasmeen Abutaleb in New York and Devika Krishna Kumar in Bengaluru, editing by Peter Henderson and Richard Chang; Editing by Sriraj Kalluvila, Richard Chang and Steve Orlofsky)