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. 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.