A teenage boy was attacked by three others during a town centre robbery.
The victim was walking along Chatham High Street towards its junction with The Brook, when he was approached from behind by the trio.
The attack happened on Sunday, at 2.35pm.
It is reported the victim was threatened before his phone was forcibly taken along with a quantity of small change.
The suspects walked off towards Best Street.
A 15-year-old boy was arrested on the same day on suspicion of robbery and assault. He was later bailed pending further investigation.
Detective Constable Martin Stevens said: "An investigation is under way into the circumstances and we are urging witnesses or anybody with information to call our appeal line."
Anyone with information should call 01634 792209, quoting reference 46/50662/23.
You can also contact Crimestoppers anonymously on 0800 555111 or by using the online form on its website.