16-year-old Julia Skala was located by officers on Friday and will now be reunited with her family, the Metropolitan Police confirmed.
Nothing had been seen or heard from Julia after she left her home in Mitcham, south west London, at about 1pm on January 8.
An investigation was launched, including house-to-house inquiries and recovering CCTV, after she was reported missing by her mother the following morning.
Met Detective Chief Superintendent Clair Kelland, in charge of policing for Merton, said: “For eleven days, we have worked around the clock to locate Julia, who was missing from her home in Merton since 8 January.
“As time passed, our concern for her welfare grew, particularly in light of the extreme cold and her lack of resources. However, following extensive enquiries Julia was located today by officers in the west London area.
“I am pleased to be able to report that she is safe and well and will be reunited with her family. This is the outcome that we were all hoping for.
“I would like to thank the media, and the social media community for their assistance with this appeal.”
There is no information or evidence to suggest she has been taken from her home address, the force said.