Are the fibres carrying live traffic? If they are not live you can trace them with a red light source, its like a pen that has a laser that operates in a visible wavelength, heres one I found which seems to use very bright LEDs:
http://feedthenetwork.com/cable-and-satellite-tv/visible-light-use-for-fiber-continuity-testing
And this one goes 10km with a laser:
http://www.dhgate.com/10km-red-light-pen-fiber-optic-test-fault/p-ff8080812b2e44e5012b48263732532d.html
With everything you get what you pay for and cheaper ones will not go as far as the more expensive ones.
With my laser based red light source I see a break in a fibre patch cord and I can also put a gentle bend in the fibre and it will leak out the side of the sheath.
I hope this is obvious but DO NOT look into the end of a connector EVER, you can't see 1310nm or 1550nm but it will give you a very cheap laser eye surgery job and will almost certainly damage them beyond repair.
If the fibres are live you may have to disconnect them to see which port goes down, thats the safest way to do it anyway.
