Do you know this man? (Credit: British Transport Police)
The victim was travelling on a c2c train from Fenchurch Street at around 9.50am on Wednesday, 17 March when the incident happened.
A man got on the train at West Ham and as it pulled into Upminster he grabbed the racing bike and ran off out of the station.
Officers have released an image of a man they believe may have information about the theft.
If you recognise him or have any information please contact British Transport Police by texting 61016 or calling 0800 40 50 40 quoting reference 2100016930.
Alternatively you can call Crimestoppers anonymously on 0800 555 111.
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