When I got back into playing I used JoinMyBand and Bandmix, then a few start ups came through word of mouth and a couple from Facebook.
I've never got anywhere with open mic nights or jam nights. The last open mic I went to, only a few months ago, was basically a lot of retired chaps warbling away whilst playing their very nice acoustic guitars. Even though I know a couple of people who run open mics it's not done me any favours, I've never got any contacts that way.
Currently I've just about given up. I got offered a spot a few weeks back in a band, the singer was in a band I was in some time back, but it was the same songs we'd been doing years ago, I'm not interested.