Hopes that missing pensioner John Harding had been seen in Tolworth since his disappearance have been dashed, after police confirmed a potential sighting was not him.
Mr Harding's family is facing a fourth agonising night without knowing where the 82-year-old has gone.
Police have released CCTV images of the last sighting of Mr Harding taken near his home.
They say call 999 if you see him - not the usual non-emergency number 101.
Mr Harding, who has dementia, diabetes and high blood pressure, was last seen at 7pm on Saturday, April 26, when he left his home in Woodland Way, on the Sunray estate in Tolworth.
More than 40 officers from Kingston police are currently assigned to the investigation, which has included a search along the banks of the Hogsmill river, close to Mr Harding's home.
Both the Metropolitan Police helicopter and Surrey Search and Rescue have also assisted in the search.
A public appeal has resulted in a potential sighting of Mr Harding entering a bookmakers in Tolworth.
But a Kingston police spokesman today confirmed the sighting was not Mr Harding.
The said: "There have been unconfirmed sightings of John, including one at a bookmakers.
"Our officers have followed up the leads and it was not John.
"We have also made a lot of CCTV enquiries but still found no sign of him."
Mr Harding is well known on the Sunray estate, having lived there all his life.
Police are asking residents living on the Sunray estate to check their sheds and gardens.
Mr Harding also has connections to Camberley and Frimley in west Surrey, although police believe the chances of him travelling that far are slim.
The spokesman added: "A lot of the search has been concentrated on parks and open space areas near to where he lives.
"He's not very mobile, and he didn't have much money on him, so we have no reason to think he's left the area.
"As time goes by we're getting more and more concerned.
"He's very distinctive chap and is well known in the community as he has lived in the area all his life. He's a familiar face in the area."
Mr Harding is five foot six inches tall, with short white hair and a mole on his forehead.
When last seen he was wearing a grey shirt, navy blue trousers and a brown three-quarter length coat.
Call police on 999 or Missing People on 116000, quoting reference 14MIS014040.