Officers are searching for a 38-year-old man from Stockton, who has been missing since Saturday.
Graham McInness was last seen by his family at around 8pm, and police have serious concerns for his welfare.
He is described as white, of slim build and is around 5 ft 9 in tall. He also has brown hair.
It is not known what clothing he was wearing.
Police have located his grey Astra, registration KU53PSY, in a car park in Seaton Carew and officers believe he was using this vehicle as recently as yesterday.
Efforts to find him are currently focussing on the Seaton Carew and Hartlepool areas, although he could have gone elsewhere.
Anyone who has seen Graham or who has information which could help police is asked to contact Cleveland Police on 101.