An 11-year-old girl was sexually assaulted while she was standing with her family at Waterloo station, police said.
The young girl was with relatives at the exit from the Tube when she was targeted by a man who touched her inappropriately.
Just seconds before the man had assaulted another woman in the same area of the station, CCTV shows.
The video footage shows the man walking past the adult victim - who has yet to come forward - and touching her inappropriately.
After the assault on the girl, her family headed to the main concourse of the station and reported the assault to police.
British Transport Police have today launched two appeals to find both the man responsible and the first victim, an unknown woman.
Officers are urging the unidentified victim to contact police as soon as possible.
Investigating officer Detective Constable Suleman Yazdani, said: “This was an upsetting assault for this young girl and we are determined to trace the person responsible.
“I am keen to speak with this man in the CCTV images; I believe he has very essential information that will assist my enquiries.
“I am also very interested to speak with another woman who was walking behind this family as I feel she was also a victim of a similar assault.
“We simply will not tolerate unwanted sexual behaviour on the underground. If you are ever a victim of sexual assault, please report it to us so we can trace and stop these perpetrators.”
Anyone with any information can contact BTP by sending a text to 61016 or by calling 0800 40 50 40 quoting reference 238 of 20/10/2016. Alternatively, information can be passed anonymously to independent charity Crimestoppers on 0800 555 111.
