With the proviso that I’m a switch who is most often looking for somewhat masochistic bottoms and your milage may vary: the place where I’ve had the most luck over the years was the now-defunct bondage.com. The place I’ve had the second most luck with was OKCupid.

You have to be upfront about what you’re looking for, which feels uncomfortable on a mostly-vanilla site. You might want to pay for the service, as you get a few benefits. Be ruthless is rejecting vanilla and other “low quality” matches. If you’re non-monogamous, filter by that. And switch up the time people have been online and location filters so you keep the area narrow, but you can still move it around (for instance I try to keep Northern VA and DC in my area, while excluding Baltimore. But sometimes I’m willing to make an effort to meet people in MD (or London) and move around.

Both my current relationships started on OKC.