There is an imageboard dedicated to professional pics of young girls in swim suits and sexually suggestive costumes/outfits. I cant remember what its called something like Candy Doll Collection or Candy Doll Chan or something. Its disgusting and since they arent nude it isnt illegal. Its really sick because the fact that they are being put in that situation in the first place can lead anyone to wonder what else is going on.
Also I once came across this Russian Photo storage/sharing site that had similar types of things sprinkled in the NSFW category. Except they were more amateur and a lot of the photo albums were password protected. The rest of the site was normal stuff but that was definitely eye opening.