Sydney Piper, aged 69, was last seen entering Lloyds Park in Walthamstow, through the Forest Road entrance, at approximately 11:50am on Thursday, 23 February.
He is described as 5ft 7ins tall, of slim build, with a grey beard and black short hair. He was last seen wearing a long black coat, grey T-shirt, grey trousers and black slippers.
Detective Inspector Jo Watts, from the missing person unit in north-east London, said: “Sydney’s disappearance is out of character and we are increasingly concerned for his welfare. He is not believed to be in possession of any money or an Oyster card and there have been no sighting of him for more than two weeks.
“Specialist officers have carried out searches of the park and we continue to recover CCTV from the area. We also need to hear from any people who use the park who may spotted Sydney over the past two weeks.
Anyone who has seen Sydney is asked to call police on 101 quoting reference CAD 4957/24Feb.