Police said they are becoming increasingly concerned for the safety of Kaylie Hatton, a 16-year-old girl who has been missing for the past week.
Chief Superintendent Jeff Boothe said they want to speak to her friends, or anyone who may have any information about her whereabouts.
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Ms Begum, now 19, left the UK in 2015 and was recently found in a Syrian refugee camp after living under IS rule for more than three years.
London Mayor Sadiq Khan said he believed "the right to peaceful and lawful protest must always be upheld".
Tafida Raqeeb's parents won a High Court battle when a judge ruled the youngster could be moved to the Gaslini children's hospital in Genoa.