At around 8.15am on December 5 the young girl was sexually assault by a man on board a train from Finchley Road to Baker Street.
When the girl then boarded another train from Baker Street to King’s Cross the same man followed and sexually assaulted her again.
On Monday (January 6) BTP released images of a man who may have information which could help with their investigation.
Anyone who recognises him is asked to contact BTP by texting 61016 or by calling 0800 40 50 40, quoting reference 469 of December 5.
If you wish to remain anonymous you can contact Crimestoppers on 0800 555 111.
