LinkedIn Corp (LNKD) forecast 2014 revenue below Wall Street’s expectations on Thursday, underscoring concerns about its ability to sustain its rapid growth and helping to drag its shares more than 3 percent lower. The social networking company, which is geared toward connecting professionals with prospective employers, foresees revenue of $500 million to $505 million this quarter, compared with an average Wall Street forecast of $505.1 million.