Actually, I did meet a woman on Adult Friend Finder a long time ago. We became friends until we had a falling out. I don't know if the site is still legit, but it was about 7 years ago. If I was to look for a casual hook up, that's where I'd sign up. But I wouldn't fork over a lot of cash.
I think most women know that advertising for sex openly is a foolish thing in today's world. It's much easier to join a legitimate dating site. You can always filter your searches to guys looking for a casual hook up. I'm sure there are plenty of them.
Plenty of Fish is free and has a very good search system. I've met a few women there. One is still a very good friend, although our relationship is strictly platonic.
Pof and ok Cupid work and are free, i'v hooked up with multable woman on both, you just got to come up with something better than "Hi" or "you wanna hook up" lol.