MD-11 First Officer reported indications of a fuel leak and the flight crew elected to divert to the nearest suitable airport to make a precautionary landing.

Narrative

For approximately the first 2-2.5 hours of flight; actual fuel in the airplane was consistently 1;000 lbs. under planned fuel at each checkpoint on the fuel plan. Then in the matter of about 40 minutes the actual fuel deficit increased to 6;000 lbs. below planned and then up to 10;000. Shortly thereafter we got a Level 2 FUEL QTY/USED CHK Alert with POSSIBLE FUEL LEAK displayed. Completed QRH procedure but could not verify the existence/origins of a fuel leak. Compared fuel at startup; burned fuel; and current fuel. Calculated that there was 10;000-12;000 lbs of fuel loss that had not been burned. Contacted Dispatch and Maintenance who also connected us to a Tech pilot. Still could not isolate the problem but knew tanks 1; 2; and 3 were not leaking based on results of QRH procedure. But; as the actual fuel vs planned fuel deficit continued to increase upwards towards 16;000 pounds; the crew agreed that the best option was to land at the nearest suitable airfield per the QRH since sufficient reserves to destination could not be verified. Coordinated with ATC and turned towards ZZZZ as the nearest suitable option. Uneventful approach and landing. After landing; there was a confirmed fuel leak coming from the tail/ horizontal stabs.Fuel leak in the tail of the airplane. Exact source unknown.