A teenager was groped on a train late at night in Surbiton station moments after her family left the carriage.
The 18-year-old was travelling from Surrey towards Waterloo with her family at about 11pm on Thursday, June 19, when the attack took place.
Police believe the attacker left the station by the Glenbuck Road exit.
Det Con Andy Parkinson, of the British Transport Police (BTP), said: "An 18-year-old girl from Surrey was travelling home from London with her family when a man sitting opposite her started looking at and talking to her during the journey.
"At Surbiton they both stood up to leave the train. After waiting for her family to exit first, the man grabbed the victim and touched her inappropriately.
"This was a very intimidating experience for a young woman who was simply trying to make her way home."
Anyone with information should call BTP on 0800 40 50 40, or text 61016, quoting reference SSUB/B6 of 17/07/2014.
Alternatively, call Crimestoppers anonymously on 0800 555 111.