About three years ago, I set up
Falkirk RPG. Initially, this was a Meetup site, then migrated to Groupspaces, and then to its current form, which we control fully. In each case, the moves were caused because Meetup and then Groupspaces made changes to their operations, or the services that they offered, that just didn't suit us.
(Along the way, one of our members took over the running of the site. Given that I was only really interested as far as finding a game, I was more than happy to give up the administration side!)
My recommendation to someone who was considering doing the same would be to go with Meetup, at least initially - they appear to be the biggest such site, and as such are the most likely to attract hits. I don't think they're the best operation, and frankly they were over-expensive for what they offered, but in the early days what you most want is hits, and they're your best bet for that.
Crucially, when you decide to take the plunge, it's very important to set up the site and schedule a first meeting
immediately. There's no way to know when a prospective player might find you, and if the site looks dead, they'll probably never be back. So don't start setting up a site until you've got some free time to work on it. Then, set up your profile, set up your site, and schedule a first meeting - and do it all before you walk away from the PC!
Your first event should be a "Meet'n'Greet" event, held in a public venue (we used a local pub). Schedule it for a couple of weeks after the site goes 'live', preferably on a midweek evening. And
whatever you do, do not cancel this event. Even if it looks like you're going to be there on your own, you need to gut it out and attend. (I had two people sign up to the site, and the M&G, almost immediately. A fourth person attended the M&G having seen the site but not yet signed up.)
At the Meet'n'Greet, your main purpose is just to get to know the other attendees. Just chat about the usual topics - a bit about yourself, a bit about them, past RPG experience, film/TV/music, etc. The other thing you should try to do is schedule another meeting, this one to get started on a game of some sort. (Be aware - if you set up the site, you need to be willing to at least try running a game.) And make sure you add that new event to the Meetup site's calendar as soon as you get home!
And go from there. One of the lessons I learned quite early is that momentum is really important. If you've got a group that looks like it's busy, it's that much more likely to see new people sign up. So, keep the site up to date, contribute to the forum, and generally keep things going. If you build it, they will come.
(Conversely, if your site looks like it's dead, nobody will bother signing up. And why would they?)
I hope that helps somewhat. Obviously, if you choose to go down that route, and if you have any questions, feel free to ask. Good luck!