Police are trying to find two males in connection to a homophobic incident that happened on the Jubilee line on October 21.
The victim, 19, was wearing fancy dress and was travelling to a party when two youths attacked him.
One of the men grabbed him, placed him in a headlock and ordered him to apologise for being gay.
The victim, who could not breathe, eventually did as they said.
The incident occured on a westbound Jubilee line train between West Ham and North Greenwich station on October 21 at around 11.10am.
The police are appealing for information in connection with the incident and wish to identify the two youths who carried out the attack.
The two youths initially verbally abused the 19-year-old for being gay but later turned physically agressive when they were challenged by the teenager and his friends.
They also snatched the teenagers phone and threatened to stab him in order to make him apologise for being gay.
The youths returned his phone when they released him from the headlock but assaulted his friend who was trying to help him. She suffered bruising after being punched and knocked to the ground.
The victims left the train at North Greenwich station.
The British Transport Police released images of the youths on December 4 and urge anyone who was involved or witness the attack to come forward.
The BTP said in a statement: “Hate crime will not be tolerated by the British Transport Police. We believe everyone has the right to travel safely."