A woman, thought to be one of three offenders, fell to the ground in front of the victim, and as he tried to help her up, he was pushed to the ground from behind.
Another man, who also tried to help the woman up, and another woman, are believed to be responsible for stealing the money.
Police have released CCTV images of three people they would like to speak to in relation to the incident.
PC Natasha Gidda, investigating officer, said: “This is an appalling incident where a vulnerable man was purposefully targeted and robbed.
“Like any honourable human being, he thought he was helping a woman who had fallen over in front of him. Little did he know that this was part of a scam to steal his cash.
“We have already carried out a number of inquiries since this robbery was reported to us. However, no arrests have been made at this time.
“I am keen to speak to the people pictured as I believe they could have information which may assist with our enquiries.”
If you have any information, contact PC Gidda on 101