There are no indications missing teenager Scott Redman is still alive, according to South Australian police investigating his disappearance following a high-speed chase earlier this year.
Police have now declared Mr Redman's disappearance a major crime and have launched a fresh search for the 19-year-old, who has not been seen since April.
Investigators are focusing their search efforts on a 12-square-kilometre area west of Kimba on Eyre Peninsula.
Police believe Mr Redman and an associate travelled to the area after abandoning an SUV which was involved in a brief police chase.
The black Kia Sorento was being pursued on the Eyre Highway near Kimba about 3:50pm on Saturday, April 21.
Police terminated the chase a short time later, and said the SUV then turned onto a dirt road.
The other alleged occupant was arrested two days later after hitch-hiking from Middleback Range, and the SUV was found abandoned at Secret Rocks about 40 kilometres east of Kimba on April 25.
But police have been unable to find any trace of Mr Redman, despite several searches.
"Investigators have not been able to find any indication that he is still alive," police said in a statement.
Mounted police will today be assisted by officers from the Major Crime Investigation Branch, STAR Group and the State Tactical Response Group, as well as local police.
"Police are determined to do everything possible to locate Scott and return him to his family, and are committing significant resources to this search in the hope of finding him," Detective Superintendent Des Bray said.
In May, police said they held "grave fears" for Mr Redman's wellbeing, after monitoring his social media accounts and speaking to friends and family.
But at that time it was thought he could have travelled interstate, with police stating that "Scott doesn't want to necessarily be found".
"It is possible that Mr Redman has also caught a lift with someone, but we have no evidence of that at this time," Inspector Mark Hubbard said in May.
Police have not provided detail on why Mr Redman was being pursued in the first place.