David Brown, 59, was last seen at around midday on Saturday 8 June 2019 in the Tonge Moor area of Bolton.
David is described as white, of medium build and approximately 5ft 6in tall. He has a mole on his right cheek and a tattoo saying "I love Jan" on his left forearm as well as dots on both knuckles.
David has vascular dementia and has missed his medication so he may be confused and disorientated.
Officers are becoming increasingly concerned for David and want to make sure he is safe and well.
Anyone with information about David's whereabouts is asked to contact police on 0161 856 5620.