Mannat Mann was last seen near Wanstead Park in Redbridge at 1.45pm on Thursday, 22 July.
She has very recently arrived in the area and has no local links.
Other than one possible sighting approximately a mile from where she went missing, there have been no other reports.
Mannat is of Asian appearance with long dark hair. She was wearing a white t-shirt and grey leggings with a white stripe when she was last seen.
She has relatives in Hounslow and may try to make her way to the area but the majority of her ties are with Wolverhampton in the West Midlands.
Officers there have been informed and are assisting with the investigation.
Detective Sergeant Gurps Singh, of the East Area Command Unit, said: “We are becoming increasingly concerned for Mannat’s wellbeing.
“She does not know the area she went missing from and we don’t believe she has tried to contact family members living in other parts of London.
“We have been carrying out extensive enquiries all day in an effort to locate her but we now need the public’s help.
“Every set of eyes is a valuable resource. I’d urge anyone who lives in the Wanstead Park area to check their dash-cam and doorbell footage from yesterday afternoon through to this evening and to contact police if they have captured any sightings of Mannat.
“We are also keeping an open mind as to whether she has travelled outside the London area, possibly back to the West Midlands.
“Our priority is to bring her home safely and any information that can assist in that effort could be vital.”
Anyone who sees Mannat should call police on 999, providing the reference CAD8090/23JUL.