Most employers can search on Facebook, Myspace, G+ using your name as provided on the employment applications anyway and they will only see what's permitted to see as an outside guest according to the privacy settings you have set on your profile. To keep employers (and snoopers) out, you should set privacy settings as high as possible, and if they try to friend you decline them or ignore them. Another good thing is to NEVER discuss work related items on social media as such posts can come back to bite you in your backside later.