The incident took place on Wednesday 4 October at about 11pm near Reading Bridge, along the promenade next to the river.
The victim was walking from the railway station towards Caversham when he was approached by a group of youths, some of whom were on bicycles.
They rode their bikes around him and when he asked them to stop, one of the group assaulted him by punching him in the face.
The victim was taken to hospital with a serious eye injury. He has since been discharged but will require surgery as a result of the incident.
The offender who assaulted the victim is a mixed race boy, aged approximately 15 or 16, and is about 6ft tall. He was riding an orange Readybike.
One member of the group is a black boy, aged approximately 15 or 16 and is about 5ft 6ins with a stocky build and black hair which was short at the sides and long on top. He was wearing dark clothing and was riding a black mountain bike.
The rest of the group included a white boy also on an orange Readybike who had a lean build and dark curly hair; a short white girl who was aged about 14 and was wearing jeans, and a white boy who was with the girl.
Investigating officer, Detective Constable Holly Stothard of Force CID, said: “As the picture shows, the victim sustained a very serious injury as a result of this assault, and he has understandably been left traumatised by this ordeal.
“This was a concerning incident, which was completely unprovoked, and I would like to appeal again for anyone who has any information about it to get in touch.
“I would like to reiterate that we are only looking for one offender in relation to this incident, but we know that there were people present who witnessed the assault.
“If you saw this incident, or if you recognise any of the people described, please call the Thames Valley Police non-emergency number on 101 and quote reference 43170294813.”