Detective Grant Miller, of Queenstown, said he interviewed a colleague of Mr Tornberg's from Queenstown's Fresh Choice supermarket who said they saw him in Beach St on Saturday afternoon with his head down, wearing sunglasses. The person did not speak to Mr Tornberg but Det Miller is confident the sighting was "legitimate".
"We're definitely still concerned. He still hasn't contacted his parents, he's definitely not following his normal routines. It's out of character," he said.
"One of the possibilities is that he's trying to avoid authorities due to the expiration of his work visa, which lapsed at the end of September."
Mr Tornberg had lived in Queenstown for about a year and his bank account and cellphone had not been used since he was last seen, although police had not ruled out the possibility he had another source of funds.
"Mr Tornberg is not in trouble criminally, in relation to his disappearance, but there are issues related to his immigration status that need to be sorted," Det Miller said.
Police would be speaking to other people who said they saw the missing man over the weekend in Queenstown.
Mr Tornberg was reported missing on October 18 after friends and colleagues had not seen or heard from him.
He is described as 180cm tall, with blue eyes and of medium build, and was last seen at his Queenstown flat on October 6 wearing a black leather jacket, blue jeans and dark-coloured T-shirt.
"We just want to know where he is. It's an unusual disappearance. His friends say it's out of character for him not to be in contact," Det Miller said.
Mr Tornberg was not an outdoors enthusiast so it was unlikely he had gone tramping; nor had he left the country.
His family in Sweden had been contacted and they also expressed concerns he had not contacted them.
Anyone with information about Mr Tornberg is asked to contact Queenstown police on (03) 441-1600.
