The leak started a month ago, I have four small openings in ceiling above the bathtub and the sink. The Supt advised me he changed the faucets and connections in the bathtub and sink,ran the water and nothing happened. With in a few days it started again. The leak has centralized to one opening, I have an 8oz plastic cup in my soap dish over the sink which the water drips into, the cup has fulled to the top occasionally.
FYI... I live in a coop building. Apt above are owners, I'm a renter. The building owns my apt.
Is there a way of detecting a leak in a pipe without breaking the wall in the above apt?
I appreciate any suggestions on what the Supt should next.

They could open your ceiling, its shot already anyway. However, do not do anything on your own. As a renter you shold not attempt any fix but keep complaining about lack of a proper fix. Long term leaks can affect your health in a very bad way.