The search for a missing teenage girl has been paused after police spent weeks scouring a river in Tasmania's northeast.

Shyanne-Lee Tatnell was last seen near the North Esk River in Launceston on April 30.

Police had been searching the river and surrounding area for two-and-a-half weeks but the 14-year-old has not been found.

Inspector Craig Fox said police have serious concerns for Shyanne's welfare.

"While the large scale search of the area has been paused, the investigation remains active and inquiries are continuing," he said in a statement on Thursday.

"We are forensically testing further items of interest that have been located over the past fortnight."

Shyanne 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 should contact police.