The man in charge of the search co-ordination, Sergeant Ian Martin, of Invercargill, said there was still a good possibility 68-year-old Raymond Horn could be found alive — but possibly in desperate need of medical attention.
Mr Horn went missing from Walmsley House, a rest-home in Richmond, on Monday.
The home was a Presbyterian Support Southland (PSS) service.
He was last seen at 8am and police were called at 1pm after an unsuccessful search in the immediate area by staff.
Residential areas, Queens Park, the railway tracks, green spaces and the Otepuni Stream had been searched; the efforts involved dog handlers and kayakers.
There was concern Mr Horn had got into trouble and needed help, such as being locked in a shed.
As the result of a stroke, he was unable to communicate verbally.
Sgt Martin said there were 11 volunteers searching for Mr Horn yesterday, but that was to increase in the evening.
This included more Land Search and Rescue teams, as well as door-knocking and Fire and Emergency New Zealand searching inner city commercial and residential buildings.
PSS chief executive Michael Parker said staff and residents were upset, but remained positive.
"We understand after four days there are concerns."
He said the home was not a secure unit, or a lockdown situation, and residents could come and go as they chose.
However, during Mr Horn’s stay, which began last August, he had not gone further than one street behind the home, Mr Parker said.
His leaving was therefore out of character, and no clues were left as to his whereabouts, he said.
"We want the community to understand it was not someone’s fault; we’ve done nothing wrong.
"We just want him back, we want to find him."
Mr Parker said Mr Horn mostly kept to himself.
Sgt Martin said while no calls from the public had yet led to anything, police had received CCTV footage that showed Mr Horn walking west towards central Invercargill from the Yarrow St, Macmaster St area about 9.30am on Monday.
Police asked people to search their properties, even if they had previously searched them.
If Mr Horn was seen, people were asked to call police and quote event number P045508171.
He was believed to be wearing a black and red jacket, and possibly a light-coloured polo shirt, gym shoes and sweatpants or jeans.
