Adam Seaton is still missing after driving to a Marshside nature reserve on August 9.
The geography student, who has turned 20 since he disappeared, is thought to have driven to the area to gather information for his course. His mother's red Ford Fiesta was later found in an RSPB car park - Adam, however, was nowhere to be seen.
There has been an intense search of the area near the car park including the use of drones and microlight planes.
There were no reported sightings of Adam getting out of the car at the nature reserve, although he is thought to have made a phone call there before his signal was lost.
Police have asked anyone with relevant information or dashcam footage to get in touch.