I would assume the same places that folks who are not celebrities do. George Michael was found to be cruising Grindr when he was in Australia.
Is That George Michael I Just Spotted on Grindr? / Queerty
I would also assume that based on your query, celebrities aren't lacking for sex, as any person with even minor notoriety or fame can score despite their looks. Hell, even Verne Troyer bagged a hot piece and made her his wife.
I live in an area where celebrities come and go fairly unnoticed because Washingtonians tend to be oblivious to pop culture, having seen Anderson Cooper at the local gay club, Beyonce and Jay Z having dinner at a posh restaurant and Angelina Jolie on her way to the museum.
I think the risk for most celebrities is too great to put any photos online so they probably hire escorts if they're desperate or just go virtually anywhere and make moves on someone, someone will bite. Your best bet is to go to all of the hotspots in LA, Miami, New York or elsewhere and look your best, flirt, and try not to seem desperate. I have a feeling they can spot a fame whore a mile away