The 41-year-old was last seen on the evening of Thursday, February 13, on Lower Bennett Street in the City.
He is described as 5ft 11, large build with dark brown short hair. He was wearing a green coat with a grey/blue Jodie under it, blue jeans and navy slip on shoes with cream laces.
Mark was last seen driving a white Mercedes Sprinter Van.
Police say he may also be in the Donegal area.
Anyone with information regarding his current whereabouts is asked to contact Police on 101 quoting 1233 15/02/2020