The incident happened around 5.15pm on Wednesday May 19 – in a move which saw the boy hand over his belongings. The thief then got off the train at Anderston station.
The man is described as a white male in his early 20s of medium build with ginger hair and a beard. He was wearing a white Tommy Hilfiger t-shirt and light grey joggers. At the time of the robbery the service was extremely busy, officers are keen to speak to anyone who may have witnessed the incident.
Witnesses can contact BTP by texting 61016 or calling 0800 40 50 40 quoting 492 of May 19.