British Transport Police have released CCTV images following a robbery at Crossharbour DLR station, Tower Hamlets.
The incident happened at around 6.45pm on Thursday 16 January.
A group is reported to have shoved a teenage boy and demanded his coat on the stairs at the station.
During the robbery, one of the suspects showed the victim the handle of a knife tucked into his waistband.
Officers would like to speak to the people in the images who may have information that could help their investigation.
Anyone who knows them is asked to contact BTP by texting 61016 or by calling 0800 40 50 40.
In both cases quote reference number 489 of 16/01/20.
Alternatively, call Crimestoppers anonymously on 0800 555 111.