Hollyoaks actor Thomas Scurr was left with a broken cheek and a fractured eye socket after being battered in an unprovoked late night attack.
The star, who plays Barney Harper-McBride, in the Channel 4 soap, was assaulted by a shaven headed thug at about 2.30am on Saturday May 11, as he walked through London's Leicester Square with fellow actor James Conway.
Scotland Yard said the pair were crossing the northern side of the square when they were approached by the attacker who was with a woman with shoulder length brown hair.
The offender, described as white, 6ft tall and stocky, launched the unprovoked attack after the two celebrities posed for photographs with fans.
Mr Scurr, 22, was treated at hospital.
Detective Sergeant Nathan Tozer, of the Metropolitan Police, said: "This was a nasty and completely unprovoked attack, which resulted in Mr Scurr sustaining serious injuries to his face, and I am keen to identify the person responsible.
"I am really hoping that members of the public who were in the area at the time may be able to help us with our inquiries.
"We know that prior to the incident several people identified Mr Scurr and Mr Conway and asked them to pose for photos, and I am keen to hear from anyone who was in the area and may have taken pictures of the pair on their phone, or noticed the incident taking place."
Mr Scurr said: "I would personally be very grateful for any information members of the public may have that would help DS Tozer with his investigation.
"Hopefully then we can find this guy and show him that there are always consequences. "