Personally, I think you'd be better off telling EVERYONE (and I mean everyone) you know that you are looking to care for a child. Networking could be key here. I don't think I would ever hire a sitter from an ad, either in a paper, or posted up on public bulletin board, but I would definitely at least call someone who knows a friend of a friend if I were looking for a sitter. KWIM?
We found the girl who watches DS for us sometimes through my hairdresser's daughter. She's a local college freshman, has a car, and is just a good fit for us right now.