well modeling is not really G4P.
Artuli Media in NYC owns MuscleGallery, MuscleWeb and MuscleHunks. The three sites differ in their explicitness. MuscleGallery is pretty benign, MuscleHunks is j/o video clips. Lots of top amatuer and pros on all three. email me for Ulrich Oehmen's contact info.
for real g4p, there's rentboy and of course craigslist.