Unless you're looking for work in fields that require stringent background checks, you don't have much to worry about. Your employer isn't going to pay for a FBI background check on you, nor bother with the paperwork of it. But, as Muad said, make sure you keep your social media accounts separate, or alternatively keep your accounts super private and be cage-y about who you accept requests from. If your employer really cares about what you're up to online, there are services they can use that will make printouts of everything you've ever done on your social media accounts (though, the content has to be public or accessible to the service.), and it's not fun to be pulled into your superior's office to be lectured about the memes you used to like when you were 15.
Other than that, your employer and co-workers won't know dip damn about you unless you tell them. They can search all they want, but they'll only find the public stuff.