I've had very bad feedback on this place -- if it even still exists.
Best thing might be just to call up one of the known entitites -- Arena, His, B&N, Aqua, Hero...whatever...and have them send someone over.
Otherwise, you can find some advertisements for freelancers at
www.gayromeo.com, as well as
www.thaimalemassage.com (but you have to register for the latter, and the postings are mostly in Thai).