Isis, from Ashford, was last seen in Stratford on the morning of Monday, October 13.
Due to the length of time that Isis has been missing, police fear she could have travelled outside of London.
Isis’ mother, Vicky, said: “Our world has stood still since Isis went missing, and we desperately want her back home and safe.
“If you have any information, no matter how small, that could help us find her then I urge you to please contact the police.
“Even the smallest detail could make a difference.”
Isis is believed to have travelled by train from Ashford to London early on the morning of October 13.
She was last seen near Stratford City, Leyton High Road, at 9.30am the same day.
Isis is about 5ft 1ins, has cropped black hair and was last seen wearing a white t-shirt, ripped blue jeans and a black coat with a fur-trimmed hood.
Detective Inspector Martin Enever, of the Met’s North East Command Unit, said: “We, and Isis’ family, are becoming increasingly concerned for her welfare.
“Even if you live outside London, take a close look at the photo of her.
“If you recognise her or have any information, please contact us urgently on 101, quoting CAD 1498/15OCT.
“If you see her, dial 999 immediately and quote the same reference.”
