Companies such as UPS, Sodexo and Taco Bell are using social networks such as Facebook, Twitter and Pinterest to help their recruiting efforts. About three-quarters of employers responding to a Jobvite survey said they made hires through social media in 2011, so firms can't afford not to have an HR presence on social networks, writes Jason Ginsburg. "Clearly, if your company isn't on these social networks, you're missing out on a large pool of passive candidates," Ginsburg writes.