Ella Whitrod was reported missing from the Bermondsey area on 21 June.
Her last confirmed sighting was in Westminster on Sunday, 16 July.
The 14-year-old has links to areas across the capital including Newham, Westminster, Wandsworth, Waltham Forest, Tower Hamlets and Hackney.
There is also information to suggest she may have travelled to Nottingham, police said.
She is described as being around 5ft4ins and was last seen wearing a black puffa jacket.
Extensive inquiries have been carried out and analysis of her phone data by officers appears to show she is still regularly using social media.
Detective Inspector Adrian Smith from the missing person’s team in Lambeth said: “Ella’s family are understandably concerned and we are keen to make sure she is safe. I would ask anyone with information about her whereabouts to contact us immediately.”
Report any information by calling 999 quoting the reference 23MIS020633. Information can also be shared with the Missing People charity by calling 116 000.
