Formspring

Formspring launched in November 2009 from the founder of a company that made online forms. It hit 1 million users in 45 days. By June 2011 it had 25 million. By early 2012 it had logged over 4 billion responses. What it did not have was enough money to run a site that size. In March 2013 it announced it was closing because it had "been challenging to sustain the resources needed to keep the lights on." A last-minute buyer saved it and renamed it Spring.me, and that died too. The address ended up redirecting to a site called Twoo. Four billion answers, and not one to the only question that mattered.