The victim was on a train approaching West Dulwich station just before 4.30pm on April 19, when a man he did not know began racially abusing him.
The man then repeatedly punched the victim before getting off the train at Sydenham Hill.
Officers investigating the attack have released CCTV images in connection with the hate crime.
British Transport Police on Friday issued two CCTV images of a man they believe “may have useful information which could help their investigation”.
If you recognise him, or have any information, please contact BTP by texting 61016 or calling 0800 40 50 40 quoting reference 422 of 19 April.
Alternatively, call Crimestoppers anonymously on 0800 555 111.