The drivers of three cars could hold crucial information about the disappearance of a 14-year-old girl in northern Tasmania more than three weeks ago.

Shyanne-Lee Tatnell was last seen near the North Esk River in Launceston on April 30 and hasn't made contact with anyone since.

Police on Tuesday asked for public help to identify three cars in the vicinity around 9pm.

They released CCTV images and footage of a silver sedan, possibly a Holden Commodore, a van similar to a Honda Odyssey and another likely silver sedan.

Inspector Craig Fox urged the drivers of the cars to come forward.

"They may have a valuable piece of information that could assist us to locate Shyanne-Lee or track her movements," he said.

Insp Fox said police had seized items of interest which would be forensically tested for any evidence of her DNA.

He didn't say what the items were, or where they were found.

Insp Fox said CCTV footage captured Shyanne-Lee running in Launceston prior to her disappearance but there was no evidence of her being chased.

The search for Shyanne-Lee was paused on Thursday after divers and volunteers combed the river for several days.

"Every time we have a missing person we do have a criminal investigation running alongside it. That has been happening since day one," Insp Fox said.

"Right now this investigation is sitting with a dedicated group of detectives.

"We always hope in any missing person investigation they are alive.

"(But) we know as this goes on … the chances of a successful outcome are getting slimmer by the day."

Police have previously said there is nothing to indicate Shyanne-Lee's disappearance was suspicious.

She was last seen wearing bike shorts and a cream hoodie with dark writing across the chest and shoulder.

She is described as being about 160cm tall with a slim build and blonde hair.

Anyone with information has been asked to contact police.

Lifeline 13 11 14

Kids Helpline 1800 55 1800 (for people aged 5 to 25)