British Transport Police officers are searching for a teenage girl who threatened a 17-year-old at Looe railway station, at around 5pm on April 8.
Investigating officer, PC Mike Phillips, said: "At Looe railway station, a 17-year-old girl was subjected to threats of violence by another girl who was in a larger group.
"The group of girls travelled on the 1715hrs First Great Western (FGW) service to Liskeard where they changed trains and travelled on the 1750hrs FGW service to Plymouth.
"I am appealing for anyone who witnessed the incident at Looe, or who may know the person responsible, to come forward with the information as you may be able to assist the investigation."
The offender is described as a white female, aged 17-18 and about 5'6'' in height.
She has red hair, which was shoulder-length on one side and possibly shaved on the other, spoke with a Plymouth accent and was wearing a multi-coloured woollen jumper, black tracksuit bottoms and tan-coloured Timberland boots.
Anyone with information which they believe can assist should contact British Transport Police on Freefone 0800 40 50 40, or the independent charity Crimestoppers on 0800 555 111, quoting incident reference number B8/WWA of 19/04/2013.