The unidentified attacker is said to have cut the 19-year-old man on the shoulder with a knife just after 10pm on Thursday in central Varberg on the west coast of Sweden, reports regional newspaper GP.
The assailant then ran off. Police dog handlers spent the night looking for a man in a yellow jacket, blue jeans and a clown mask, but he had not been found by Friday morning.
Ambulance workers called to the scene described the teen's injury as minor.
Several other clown-related incidents have been reported in Sweden in the past few days on the back of a worldwide 'killer clown' trend starting in the US, mirroring a spike seen in France and Spain two years ago.
“We don't know what preceded this,” police spokesperson Ulla Brehm told GP. “It was not a robbery and I don't know if they had argued before. It's hard to say if this is something to do with this trend from the US, but there was a clown mask at the scene.”
As The Local reported on Thursday, a pair of knife-wielding clowns threatened a woman in the small town of Skänninge near Mjölby in Östergötland shortly after midnight yesterday.
With clown sightings multiplying this month in the UK, British police this week asked people not to go outside dressed as clowns. And Swedish authorities have warned people not to participate in the trend.
“We don't want a person to risk serious problems because they, perhaps partly for fun, put on a clown mask. Because obviously after what has happened in other countries, the police will be on their toes,” Interior Minister Anders Ygeman told the TT news agency on Thursday. “It's Halloween in a few weeks and that's a weekend on which we don't want any tragic misunderstandings.”