I only skimmed the responses so far, so if I'm repeating please forgive me.
To troubleshoot my system I tried to isolate as many different areas as possible. I have a 4-way manifold split coming off my regulator, with valves on each line. So first I pressurize the whole thing, with no kegs connected. then I close all the valves on the manifold, close the tank valve, the valve at the output of my regulator. Then I wait a day or two.
I then go through each quick disconnected and open it with my finger. If it has pressure, that means that section is okay. So I can check each leg of the air lines from maniforld down to the disconnects for leaks.
Then once that is done, I open one of the manifold valves. if I hear the air hiss of pressure equalization then I know I'm ok up to the valve on the output of my regulator because the manifold was still pressurized. Then I open the regulator output valve. If I hear another hiss, then the regulator itself is okay.
For kegs I just pressurize and disconnect. Burp them the next day to see if they're still good.
YMMV, but I've had pretty good success with this method. At first I tried soapy water, but that just made a mess inside my keezer and didn't find my leak.