Your average cop walking the beat or patrolling neighborhoods isn't going to be looking at online sites hoping to crack some big steroid ring wide open. The feds, sure. Do they have better things to do? I'd think that they have certain departments and assignments like, white collar crime, bank robbery division, counterfeiting, drugs, and yes.....I believe steroids ESPECIALLY with all of the press it's been receiving these last few years in sports, President, etc...
Think about it...if you were a fed, would you simply join or visit a gym and hope to find some big dealer there? Not that many people would care about a story of a local guy that gets busted for selling some roids out of a gym as opposed to an international operation. It's easy to come online and read everyone's confessions, see pictures of themselves posted, and come across a few sources. We're not in some small back room where you need a secret knock to enter, we are openly posting on the internet for the whole world to see. Yeah, I'd think they're here.
p.s. make sure you kiss your source for taking the risks that they do.