A 17-year-old girl was sexually assaulted twice, by two different men, while travelling home from a music festival in Cornwall.
British Transport Police (BTP) say the "shocking" assaults happened between Newquay and Plymouth on Saturday 12 August as the teenager was returning from the Boardmasters music festival.
Officers say that the first man, who was wearing a novelty shark hat at the time of the incident, asked her if she wanted help with her luggage as she boarded the train at Newquay station.
The man was said to have started tickling the girl after she refused to kiss him and trying to take her phone, so she moved seat.
It was then that she met another man and explained to him what had just happened.
The second man then started sexually assaulting her by kissing her and touching her inappropriately and then himself inappropriately.
BTP say the incidents happened between 8.45pm and 9pm as she tried to make her way home.
The first offender is a white man with pale skin, ginger hair, he was wearing a white shirt with a palm tree on it and blue shorts with a novelty shark hat.
The second offender is a white man, with mousey hair and pronounced sideburns. He had a white polo shirt on and camo shorts. He gave his name as Lance.
Investigating officer DC Matt Grieve, said: "This was a deeply upsetting and shocking incident for this young woman and we are urgently seeking witnesses.
"If you were on board this train and witnessed what happened, or saw two men acting suspiciously, then I would urge you to get in touch.
"Your information could prove vital in our enquiries to understand what happened, and who is responsible."
Anyone with any information is urged to contact BTP by sending a text to 61016 or by calling 0800 40 50 40 quoting reference 423 of 16/08/2017. Alternatively, ring Crimestoppers anonymously on 0800 555 111.