Police investigating the disappearance of 15-year-old Maddie Thomas are now treating the case as child abduction.
The teen, also known as Madison, left her foster parents' home in Southmead, Bristol, saying she was going to the shops on 26 April and has not been seen since.
Detectives now believe she is likely to be with a man.
Detective Inspector Laura Miller said: “We are no longer investigating Maddie’s disappearance as a missing person case but as a child abduction.
“When Maddie has previously gone missing she has been found in the company of adult men and it is mainly due to this history that we believe she is likely to currently be with someone.”
Watch: Police release video footage showing the last known sighting of missing 15-year-old girl
Avon and Somerset Police have stepped up their appeal to locate her, showing video footage of her feet recorded at 2:43pm on Stanton Road, Southmead.
Police say they will also be going door to door to ask residents if they know Maddie or have seen her, while leaflets will also be distributed.
Maddie was described as white, about 5ft tall and of an average build with shoulder-length brown hair.
She has been known to use social media to meet people who can give her a place to stay or money - in the past having been found with men in hotels.
DI Miller added: “Maddie is a child in foster care, no one has permission to keep her from her carers. She is vulnerable and at risk of being taken advantage of.
“We’re really concerned about her safety and have a dedicated team working extremely hard to locate her.”
She said they had received several lines of inquiry and needed more help from the public to help find Maddie.
DI Miller also pleaded with the schoolgirl to get in touch if she saw the appeal and added she could be anywhere in the country.
Anyone who sees Maddie is asked to call 999, quoting reference 5222098703.
Those who have information about her whereabouts or spots her online is asked to call 101, quoting the same reference number.