If you plan to take advantage of social media venues, like Facebook, to conduct background investigations, the most important first step is to have a policy, and make sure candidates are aware of it, said Mavis.

"Let candidates know you are going to do background checks so you can do it properly and get authorization," she said.

That means disclosing all of the places you may go searching for information about a potential hire, and all of the things you may go looking for.

"Identify ahead of time the five or ten things that, if you saw them on a candidate's profile, would concern you about them. That might be a reference to use of illegal drugs, or graphics promoting hate," said Mavis. "Also figure out what might be some positives you would seek, such as a candidate who is active in their community, or involved in a cause, such as cancer research."