The terrifying incident happened as the 13-year-old was getting off a train in Greenock.
Three men approached her from behind and push her from the train and grabbed her bag.
British Transport Police said the gang then stole her smart phone and threw the bag back at her.
It happened on the Wemyss Bay to Glasgow service on Monday afternoon.
The train was pulling into Whinhill when the fiend struck at around 4.30pm.
All three men are described as being in their early 20s.
Officers are currently reviewing CCTV in a bid to identify the culprits.
Witnesses, or anyone with any information that may assist the investigation, have been urged to contact police.
It is understood the girl was unhurt, but left extremely shaken by her ordeal.
A British Transport Police spokesman said: "At around 4.30pm yesterday, a 13-year-old girl was pushed off a train at Whinhill Station.
"Her bag was then taken from her, her smart phone stolen, and her bag thrown back at her.
"Inquiries are underway to trace the three males responsible.
"They are described as being in their early 20s and officers are checking CCTV footage."
Anyone with any information to contact British Transport Police on 0800 405040.