A 15 year old boy sustained injuries to his back and face during the incident which police have described as a vicious assault.
They are also asking motorists who may have a dash cam fitted to their vehicle to check the footage.
Inspector William Calderwood says they would appeal to the man who stopped his vehicle and drove the victim home to get in touch.
Inspector William Calderwood said Police received a report yesterday that at around 10:10pm on Saturday night, a 15-year-old boy was walking along Rossdowney Road with his friends when they were stopped outside a shop by a group of approximately 30 youths.
One of the males in the group, described as being at least five-feet six-inches tall with brown hair and a blonde fringe, aged 16 or 17 and wearing glasses, stopped and spoke to the boy before calling over three other youths who were with him before assaulting the teenager.
The victim received treatment for his injuries in hospital after receiving a number of kicks to his head, face and back and a punch to his face. His shirt was also ripped off him.
Police say the attack ended up on the middle of the road where, at some point, the victim was able to get to his feet before a member of the public who was driving a white jeep-type vehicle stopped and took the victim home.
Waterside Councillor Christopher Jackson says the Waterside cannot be made a no-go area for anyone. He believes incidents such as this escalate as the Marching Season approaches........