I have a 2nd floor shower that is leaking onto the ceiling of thr 1st floor. What are the possible causes and how do I troubleshoot this problem?

You must first open up the ceiling to determine exactly where the leak's coming from. Cut a square out of the ceiling and save it. After it drys out it can be taped spacked and painted back in. Feel around the trap raiser. Is there moisture near the upper part of the trap? No? The look around the outer edges of the base. Is it coming past the base on the outside? Let me know. Tom