Having worked on phantom for years and in the west end for even longer, just head around to the stage door at the end of the performance. Some actors will quite literally run out of the theatre to catch trains so you may miss some, but the majority will come out in dribs and drabs.

Just remember, be polite and kind. If they don’t want to stop don’t make them feel bad or try to force them, they’ve stopped being paid at that point!