If you're near a big city or suburb, try and app called Feeld. The swingers sites mentioned above are good. Kasidie and adultfriendfinder are too, if you really have size and a good body. A decently written profile and a balance of different types of pics are needed too. Don't just do dick pics.
Fetlife is free, but you have to put in the time to seach for groups in your area there. It's like kinky Facebook. It is not specifically for hooking up, but everything happens.
There's an app called Pure that I've wanted to try. It means "purely causal sex".
