Mr Diver, who is 39, was last seen in the Townsend Street area last night. He is described as being abut 5ft 7ins tall, of a slim build and with brown hair. He has tattoos on his neck.
Police and other emergency services have been carrying out searches in the town including a search of the River Mourne.
The search of the river followed a report that a man fell in last night.
Anyone who has seen Mr Diver since about 10pm last night is asked to contact police on 101.