Police have launched an urgent appeal into the whereabouts of man now believed to be in Darlington.
Officers have become increasingly concerned for the welfare of the 51-year-old who went missing on Saturday morning.
Mark, whose surname has not been given, was last seen in Hull, East Yorkshire, but he is now believed to be in the Darlington area.
He is described as medium build, with a shaven head and wearing glasses.
He is believed to be wearing dark blue jeans and a blue jacket.
Anyone with any information is asked to call Durham Constabulary on 101, quoting incident reference number 232 of October 1.
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