The man was on board a train approaching Bromley South station on May 6 at around 11.30am when a stranger approached him.
According to the British Transport Police, the disabled man was attacked and then had his phone stolen.
The victim was left “shaken and extremely distressed”, said the force.
An image has been released of a man who police would like to speak to, as they believe he may have information which could help their investigation.
Anyone who recognises him is asked to contact British Transport Police by texting 61016 or by calling 0800 40 50 40, quoting reference 245 of 6 May.
Alternatively give information anonymously to Crimestoppers on 0800 555 111.
