Five people arrested by police investigating the disappearance of a student from Walsall have been released without charge.
Zoya Anwar, 18, was last seen by friends at King Edward VI School in Handsworth, Birmingham, on 26 February.
West Midlands Police said she was not reported missing until Friday and they were concerned for her safety.
Four men and a woman, aged between 27 and 48, all from the Walsall area were arrested on suspicion of kidnap.
Police said they were all known to Zoya and their release came after several sightings of the teenager in the Digbeth area of Birmingham on Wednesday.
Despite the sightings, officers said she had yet to be found and urged anyone with information on the student's whereabouts to come forward.
She is described as Asian, of slim build, 5ft 6in tall and with shoulder-length black hair.
Police said the "straight-A" student was due to pick up her A-Level exam results from King Edward VI School on Thursday.
In a statement, Elisabeth Wager, head teacher at the school, described Zoya as an accomplished pupil with an "exemplary school record" and "a bright future ahead of her".
"She has firm friendships in the school and we are providing support as required to her friends and the wider school community," Ms Wager added.
Det Supt Jo Chilton said: "Zoya has never been missing before and it is very out of character for her.
"Whilst we are keeping an open mind, we are very concerned for her and need to know she is safe and well as a matter of urgency."
She said police had been looking into a number of possibilities over her disappearance, including her running away from home or being taken against her will.
There had been unconfirmed sightings of the missing teenager on Friday.
Det Supt Chilton said one sighting had placed her near a Birmingham railway station.
West Midlands Police has set up a dedicated call centre for anyone with information about her disappearance.