Celebrities are tricked, kidnapped, or blackmailed into doing porn. Could be a variety of ways: mind control, non-consensual, etc. They could hate it or love it.
I see this idea done quite a bit in quite a bit of different ways. This pitch is kind of vague, too. Also, Personally, I find using real-life names and people to be rather creepy, and it's probably illegal in some places. Not trying to discourage you from writing, just my two cents.
I have one draft where basically freeuse has become so commonplace that celebs need “training” to “act” out these newly required scenes better. It’s a bit silly but I’ll finish and public it someday.
I see lots of mind control and ENF stories with celebrities. There seem to be fewer of the other types mentioned though. It could be interesting depending on how it's done.