In particular, they would like to trace two men who stopped at the scene and helped to lift the motorcycle, but then carried on their journey.
Just after 6pm on Saturday 11 June, the motorcyclist, who was riding a blue BMW 1100 RT motorbike, was travelling towards Castleton on the road between Hutton-le-Hole and Castleton.
The rider, who is from the local area, hit the grass verge and came off his bike, sustaining serious head and chest injuries. He was airlifted to James Cook Hospital in Middlesbrough where he remains in a serious but stable condition.
The collision occurred approximately one-and-a-half miles north of the Farndale junction towards Blakey Ridge. Two other vehicles, a silver Ford Fusion and a blue-green Fiat Punto were involved in the incident, although at this stage, there is no evidence to suggest any contact between any of the vehicles.
Investigation officer TC Richard Hammon said: “It’s very important that we trace any witnesses to the collision, in particular the two good Samaritans who stopped to help at the scene prior to the police’s arrival.
“The route is popular with bikers and tourists and we appeal to anyone who was in the area on Saturday evening and either witnessed the collision or saw the vehicles prior to the incident, to please contact us.”
Anyone with information is asked to contact TC Hammond on 0845 60 60 247.
No-one else was injured during the collision.