The teen was walking on Manchester Road between Preston City Centre and Avenham on Friday (March 26) at around 2.15pm when he was assaulted by four other teens.
The boy was left bleeding with a broken nose and a broken jaw, after being struck to the face with a hammer. The boy's attackers then ran off towards Laurel Street.
The suspects are described as Asian, aged between 14 and 18, and dressed in black.
A spokesman for Preston Police said that a forensic examination of items recovered from the scene was being carried out, but officers would also like to see any CCTV or vehicle dash-cam footage that may be available.
The spokesman said: "This was a serious assault which has left a young victim with substantial injuries. We are confident that forensics and CCTV enquiries will identify those involved, so would urge the offenders to come forward and speak to us.
"Anyone with any information is asked to contact [email protected], regarding log number 0826 of March 26."