The incident happened on the railway bridge on Ashley Road at around 1.50pm on Saturday 20 July.
A 53-year-old Bournemouth woman was approached by a man who grabbed her handbag, took out her purse and ran off.
The victim, helped by a member of the public, pursued the offender who ran in the direction of the bus station turning right onto Tower Road toward Palmerston Road.
Another man managed to stop the robber and recover the stolen property. During this confrontation the suspect’s T-shirt was removed.
Detective Constable Neil Third, of Bournemouth CID, said: “I am appealing for any witnesses to this incident and anyone with information about the man responsible to contact police. I would also like to hear from the member of the public, a man, who assisted the victim in her pursuit of the offender.”
The suspect has been described as white, aged in his late twenties, around six feet tall, of slight build and tanned. He has short brown hair and was wearing a charcoal T-shirt and grey shorts.
No arrests have been made.
Witnesses and anyone with information should call Dorset Police in confidence on 101 quoting incident number 20:322. Alternatively, call the free and anonymous Crimestoppers line on 0800 555 111 where mobile phone tariffs may apply.