Good question! The go-to place to start is also probably the most frustrating – Collarspace. Logging on as a female, you average about 100 messages an hour, and that’s if you don’t respond to anyone. And, of course, a great many of the profiles are fake, so really pack your patience. The reason why we keep going back is that enough of the profiles are real, and the traffic is high.

Fetlife is another good option. While it’s not a dating site per se, it’s an excellent community hub. I’d also recommend Alt.com. It’s free to set up a profile, and the process is surprisingly thorough. But in order to respond to someone you’ll need to upgrade your account. I’ve not been there for a while, but the last time I was there I remember the rates were reasonable and the traffic was steady. Also, because a modest fee was involved it tended to cut down on the fakes, unlike Collarspace.
Good luck!