Police say the case remains a missing person investigation.
Detectives investigating the disappearance of Owami Davies have made a further arrest.
A 22-year-old man was arrested by officers at an address in Croydon on Wednesday on suspicion of murder.
Three other men were previously arrested on suspicion of murder as part of this investigation, and all remain in custody.
Student nurse Owami Davies from Grays, Essex, was last seen at just after midnight on Derby Road, West Croydon, on Thursday, 7 July.
In a statement, Owami’s mother Nicol Davies said, “This is such a terrible time for all those who love Owami and I am pleading for anyone who can help find her to contact police. Every day we hope to hear the news that Owami is coming back to us, your help might make it so.”
A white van.
Detectives are also continuing to appeal for the driver of a white van that was parked in Derby Road at the time Owami was last seen.
Owami was in the company of a man and crossed the road just as the van pulled out. The van driver would have had a good opportunity to see them both clearly and officers are appealing this possible witness to come forward.
Detective Chief Inspector Nigel Penney from the Met’s Specialist Crime Command leads the investigation and explained, “While a further arrest has been made, this remains a missing person investigation and our priority is, and has always been, finding Owami.
“I would continue to appeal to anyone who has information about Owami’s whereabouts to please get in contact with my team. If you don’t feel comfortable speaking to police, then you can call the independent charity Crimestoppers – they will not ask for your identity and will not trace your call.”