Most Helpful Guy
Be straight forward and say as it is that some friends found profile on some dating site with pics on him and whet he has to say about it.
Also try make a profile on the same side with a pic on you and send him a message that he seems familiar.
If it isn't really him you can get that profile cancelled from administration of the site, if it is him his busted and know you know. you can ask insted on the site "why do you feel the need to be here?"