Yes, there is sex everywhere in Bangkok. The women who hit the bars and freelance at the clubs probably don't need a site. But the internet sideliners and WeChat/Line girls could probably use a site. There are Thai language sites (such as
https://www.dek24sideline.com/forum.php), but they're not too accessible to those of us who cannot read Thai well. And I don't know how easy it would be to hook up with these ladies via phone.
But why work so hard? Just go to a bar or get a massage...
Have fun, CGP