Officers are growing increasingly concerned for the welfare of dementia sufferer Leocardo Loney, 83.
Leocardo was last seen at about 17:35hrs on Thursday, 3 August by staff at his care home in Wembley.
The CCTV footage shows Leocardo leaving the care home and since then there has only been one possible sighting of him, on a route 182 bus travelling from the Wembley area towards Brent Cross, on Tuesday, 22 August.
Leocardo has now been missing for three weeks and his family and police are very worried about him.
He is black, about 5ft 10ins and of medium build with short grey hair.
At the time of his disappearance, he was wearing a red baseball cap and a black jacket.
Leocardo likes to take the bus and train and also enjoys going to the park and betting shops in the area.
He needs medication for his dementia and may be confused.