Twitter shares could add to strong gains this year as the World Cup spurs engagement and continued strength in ad sales gives the social media company a revenue boost, an analyst at UBS said Thursday. Eric Sheridan raised his price target on the stock to $52 from $36, implying 11.2 percent upside from Thursday's close of $46.76. Twitter's stock rose as much as 2.2 percent before closing down 2.1 percent.