Zoya Anwar - who is described as a "straight A student" - was last seen by friends on Tuesday February 26 when she said goodbye to them at the school gates.
Her disappearance was not reported to police until last Friday, which prompted officers to launch a missing person inquiry.
The five people arrested on suspicion of kidnap in connection with Zoya's disappearance are all known to the 18-year-old.
House-to-house inquiries and forensic searches have been carried out over the last few days and remain ongoing.
A dedicated call centre set up to allow people to pass on information about Zoya's disappearance can be reached on 0800 092 0410.