John Mullings, 86, was last seen at his home address in Holloway, at 09:00hrs on 1 December.
He is a white man, around 5ft 10ins tall of slim build. He wears glasses and a missing lower left tooth.
He was wearing a beige and brown check flat cap, casual black jacket, grey jogging bottoms and black polished shoes.
Officers are concerned for his welfare as he suffers from health problems.
Anyone with information is asked to call CID at Islington on 07766 781861 or the police non-emergency line on 101 quoting reference CAD 5845/1DEC15