Luke Durbin, 19, of Hollesley, Suffolk, failed to return home after a night out in Ipswich on 12 May 2006.
His mother Nicki said when a police team took over the case and interviewed her for six hours she was able to put more emphasis on the car.
She had always believed the owner of the Volvo car was significant.
"I am hopeful someone will now come forward and I am convinced there is someone out there with relevant information," she said.
"Despite the disappearance being nine years ago I am sure someone locally knows something.
"It's a relief to know the team is now looking seriously at the importance of the car."
Police know the silver or white Volvo 440 was seen in Orwell Place in Ipswich at 04:19 BST on Friday 12 May 2006, just minutes after the last CCTV images of Luke .
Officers are keen to trace the driver and any occupants of the vehicle.
Mr Durbin had spent part of the evening in Zest nightclub on Princes Street before leaving in the early hours.
The last sighting of him was on CCTV walking across Dogs Head Street in the direction of the bus station.
Det Supt John Brocklebank said: "Someone locally knows what happened to Luke, however we are still waiting for the crucial piece of information that can solve the mystery.
"We're releasing the CCTV images of a Volvo seen in the area.  Despite appeals we have not been able to trace the occupants of this car.
"We'd like to hear from anyone who knows someone who had access to a silver or white coloured Volvo 440 around May 2006 who may have been in Ipswich around 04:00 BST that day."
The family of a teenager who vanished nine years ago has welcomed a police appeal for information about a Volvo car seen on the night he went missing.