The boy was hit on the head at 9.45pm yesterday on Almswall Road in Kilwinning, North Ayrshire, after an altercation took place between him and a group of young people, police said.
He was taken to Crosshouse Hospital in Kilmarnock, East Ayrshire, for treatment and has since been released.
CCTV images from the area are being reviewed by officers and door to door enquiries are being carried out.
Police would like to speak with three young men aged around 16 and 17-years-old who are understood to have been in the area at the time.
One was wearing a white hooded top, another had a red tracksuit, a black body warmer and a blue baseball cap while the third teenager was wearing a red, white and blue tracksuit top.
Detective Sergeant John Deans said: "I am appealing for people to come forward, I know that this area was particularly busy last night - there was a party at Orange Halls so there would have been a lot of people around.
"A young boy has suffered a head injury in an unprovoked attack so if you were in the area at the time or you have any knowledge of the suspect or the crime, please do get in touch with us."
Police ask that anyone with information contact CID officers at Saltcoats on the police non-emergency number, 101, or call Crimestoppers on 0800 555 111.