The vehicle was stolen from Teesdale Architectural Stone, which is based at Shawbank Quarry, on Staindrop Road, sometime overnight on Saturday, June 28.
It is believed that the thieves removed the truck from the premises using an inadequate trailer.
The stolen vehicle has been described as a red Linde H40D forklift.
PC Jonathan Robinson, from Durham Police, who is investigating the incident, said: “We think that the forklift was taken away on a trailer which was inadequate for the job, as it left gouge marks on the road as it left.
“The truck’s forks bend downwards slightly, making it easily identifiable if located.”
The trailer is thought have headed onto the A688 and driven off in the direction of Stainton Grove after leaving the scene.
Anyone who saw anything suspicious around the time of the theft, or who has information on those responsible or any other information that might help officers investigating the theft, is asked to come forward.
Witnesses can call Durham Police’s non-emergency number, 101, or Crimestoppers, anonymously, on 0800-555-111.