The victim was walking along Winifreds Drive, near to the junction of West Avenue, in Donnington when he was confronted by three men.
Police say it is believed they threatened him with a knife and threw a powder over his face, causing irritation to his eyes, nose and throat.
They then pushed him to the ground before stealing his mobile phone, push bike and other items.
The first suspect is described as white, 6ft 2in, stocky and was wearing a grey army jacket and black jeans.
The second was also white, 6ft, slim and was wearing a grey tracksuit, while the third was white, 5ft 5in and of big build.
All three suspects wore black bandanas with their hoods up.
West Mercia Police is appealing for anyone with information to come forward.
The robbery happened on Saturday, September 4, between 8pm and 10pm.
Detective Sergeant Richard Cowley said: “This incident was understandably very frightening for the victim and I would appeal to anyone with information to get in touch with us.
“If you were in the area of Winifreds Drive on that Saturday evening please cast your mind back to try and recall if you saw anything suspicious or if you may have noticed these three suspects.”
Anyone with information is asked to call the investigating team on 01952 214606, quoting incident 22/81351/21, or report it online at westmerciapolice.uk/tua/tell-us-about.
Alternatively, call Crimestoppers on 0800 555 111.