A teenager had his mobile phone stolen by three young men in Maidenhead on Friday.
The 12-year-old was waiting with a friend at Furze Platt train station in Harrow Lane when they were approached by the trio.
One asked to borrow the phone, and after the victim handed it over the man refused to give it back, threatening him with violence.
The three men then left the station with the phone.
The incident happened shortly before 2pm.
British Transport Police (BTP) are following several lines of enquiry, including looking at CCTV, but are appealing for witnesses.
Detective Constable Martin Coburn, investigating, said: "There were other people present at the station at the time, who we believe may have key information about what took place.
"I would encourage anyone who has any information about this incident to get in touch with us, as any information, no matter how insignificant it may seem, could really help."
Contact BTP on 0800 405040, quoting 341 of 12/04/2013, or call Crimestoppers on 0800 555 111 with information.
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