Well Pump Runs Continuously
I do not have a well, and not a water expert, but I have a recurring water leak problem and thought I'd share my experience in case it helps.  I recently experienced a problem similar to what you described - water kept running but nothing I could touch was leaking.  I could hear water running (high pitch sound), but could not locate the leak.  I finally checked under my house, in a crawl space, and it was very wet.  It turned out that the leak was underground in a rusty old galvanized  pipe.  I am still cursing that P.O.S. and the fact that any fool ever used galvanized rust prone metal.  

One other way I've been able to detect water leaks is by using a cheap stethoscope.  I once had a very expensive plumber come out with an electronic stethoscope attached to a read-out, but since then have been able to narrow in on leaks in walls by using the stethoscope (and saving myself about $1000 / event).