Officers are searching one location at the North Esk River and another in bushland near Nabowla in the state’s north-east.
The latter location covers more than 50 square kilometres, Tasmania Police Northern District Commander Kate Chambers said.
A team of about 160 search and rescue personnel are on the scene, while a cadaver dog on loan from NSW Police is being used in a search of the North Esk River.
Shyanne-Lee was last seen near Henry Street, in Launceston, near the North Esk River, at about 8.30pm on Sunday, April 30.
It’s the largest search operation ever seen in northern Tasmania, including helicopters, motorbikes, ATVs, drones, and horse riders.
The Australian Federal Police has also provided ground-penetrating radar resources.
Detective Acting Inspector Andrew Hanson said that police were following a specific line of inquiry based on information received.
“In recent weeks, we’ve successfully identified all the vehicles of interest that were captured on CCTV in the Henry Street area, travelling towards Launceston, around 9pm on 30 April when Shyanne-Lee was last seen,” he said.
Read Related Also: We've just had the hottest-ever day in recorded history
“All drivers have now spoken to police.
“We’ve searched the North Esk River several times – utilising helicopters and ground search and rescue crews, with the help of volunteers on foot, horseback and ATVs.
“Our investigative team has spent considerable time scouring CCTV, interviewing witnesses, and meticulously following up every lead.”
Hanson said that the searches were expected to be ongoing for several days.
Shyanne-Lee is described as being approximately 160cm tall, slim build with blonde hair.
At the time she was last seen, she was wearing a cream hooded jumper with dark-coloured writing on the chest and shoulder area.
She was also wearing bike shorts.
Information can be provided anonymously.