An 18-year-old man suffered serious facial injuries when he and his girlfriend were attacked by a gang in a Surrey park.
Surrey Police said the student and a 15-year-old girl were set upon by a group of youths as they walked through Sythwood Park, Woking.
One member of the group snatched the girl's bag, urinated on it and then set it alight.
The youths then kicked and punched the man when he tried to call the police.
Surrey Police said the 18-year-old suffered a broken jaw during the attack on 6 October and the girl received cuts and bruises when she tried to pull the offenders off her boyfriend.
A spokeswoman for Surrey Police said: "This was a totally unprovoked attack in broad daylight on a young couple who were just going about their everyday business, making their way home after school.
"It was a vicious assault which led to serious facial injuries and Surrey Police will not tolerate this type of brazen violence in our neighbourhoods.
"I am asking anyone who may have been in the vicinity at the time of this despicable offence to contact officers."