We had our 20th HS reunion a couple of years ago, and fb was a big part of the process for finding people. I've been in regular contact with the group of girls I hung out with in HS ever since, and I chat with some of the fellas from time to time although it's mainly the girls. In fact, we're having a get together in a couple of weeks for one of the girls who now lives in Nigeria but is coming back for a visit. We usually try to catch up every few months now and keep up with each others lives. It's actually really nice because most of these girls have seen me at my worst, as I have them, so we know what we're getting, and really, no one has changed that much from HS. They're still the same people with different bits filling in their lives. It's nice.
I'm having a catch up with a girl from HS on the 15th who I was not that close to at HS, but we've been keeping in touch via FB since the reunion. I'm looking forward to it. She was always nice at school, but just not in the group I hung around with mostly.
I say go for it. Nothing ventured nothing gained. You might just re-establish old friendships and find they still have great value in your life. If not, you can laugh at the fat cheerleaders instead.