Teen indecently assaulted on Sydney train

A 17-year-old girl has been indecently assaulted on a train in Sydney.

The teen was travelling on a crowded train between Strathfield and Ashfield stations on Wednesday morning when a man standing next to her put his hand up her skirt, police say.

They're appealing to the public to help find the man, who's described as being around 30 years old, with short black hair, and who was wearing a black top and sunglasses.