B757 First Officer reported a fuel leak that resulted in a divert and overweight landing.

Narrative

Fuel Leak was observed 1 hour into ZZZ1-ZZZ2 Flight Segment. The flight was planned for a maximum weight landing in ZZZ2. The cruise speed was systematically increased to give a projected landing fuel load of ~500 lbs below max landing weight. If there was a fuel leak in the early portion of the flight; it may have been hidden due to our dynamic planning and the fuel coming from the center tanks. Shortly after completion of center tank fuel burn off; a scratchpad message indicating a difference between measured and calculated fuel state indicated that there was an anomalous fuel state. We noticed a near 1000 lb wing tank fuel differential immediately; and saw that the measured and calculated fuel used had a differential that was larger than this. Control of the aircraft was exchanged to myself; the FO; and the captain began to run the Fuel Leak non annunciated procedure. Controls were exchanged again to allow me to go after and look for visual indications. Looking the wing through one of the bulkhead windows revealed a mist trail that I would describe as 2 feet in diameter and opaque with a quality to condensation trails that for when landing in high humidity areas. Back in the flight deck I reported I was able to visually confirm that I could see fluid leaving the aircraft. The fuel imbalance and anomalies had grown; and procedure directed shutdown was accomplished. The aircraft was prepared for an overweight single engine landing in ZZZ on the longest runway available. An unremarkable landing was completed and after inspection by emergency services; we continued under our own power to the remote parking location. After approx 1 hour of ground delay; passengers began disembarking via air stair. I went into the terminal to provide an early morning representative for the company; and the captain remained onboard the aircraft. There were significant delays in unloading passengers and baggage due to limited ground resources. The aircraft was secured by the captain roughly 4-5 hours after landing.