Sounds like the leaking water is from the drain of the upstairs neighbor tub/shower unit. This is quite likely the responsiblity of the homeowners association. You better speak up quickly to save on limiting damage and cost of repair. If this is a brand new condo, there should be warranty from the builder? Check into that.
Getting back to the leak, perhaps, there's a removable panel upstairs by the tub/shower unit to access the tub/shower supply and or drain. Maybe this could be removed to inspect the origin of the leak. (Saving in cutting holes in your ceiling)