Mya Recardo, 16, has been missing for more than a week and her family desperately want to hear from her.
She was reported missing from Beckenham in Bromley on Sunday, September 17.
It is thought that she may have travelled to Kennington, although officers believe she might be trying to make her way to the Manchester, Yorkshire or Bedfordshire areas.
She also has connections to the Stratford and Ilford areas.
A Metropolitan Police spokesman said: "Mya is believed to have left the facility she was staying in with another female, who has since been found and has informed officers that Mya expressed she may change her appearance so that she is not identified.
"Mya may now be wearing a white hijab in an attempt to alter her appearance. She also has a short black wig she may be using, a blue zip hooded top, a grey tracksuit, and a white jumper with lace down the side.
"It is possible that she has since purchased other clothing."
Mya is described as white, 5ft 5in and slim, with long black hair.
She was last seen wearing a white long-sleeved top, grey trousers, black footwear and a blue jacket.
Mya was carrying a black handbag, but did not have an Oyster Card or mobile phone with her.
The spokesman added: "Officers and Mya's family are very concerned that she may be at risk of exploitation and ask that she make contact.
"Mya has epilepsy and is currently on medication for this. There are also concerns for her mental health."
Anyone who has seen Mya or has information on her whereabouts is urged to call Bromley Police via 101 or Missing People on 116000.