The 60-year-old Italian man was fined and ordered to pay damages to the 14-year-old girl, whom he was accused of kissing on the mouth and caressing in a Zurich hotel room, reported news agencies.
The incident dates to October 2016 when the girl accompanied the man to his hotel room to look for a book on clowns.
The defendant denied that anything sexual took place between the two, with his lawyer saying the teen made up the accusations.
However the court believed the teenager, saying her version of events was credible and without contradiction. She had no reason to falsely accuse someone she had previously idolized, it said.
Video surveillance footage from the hotel and some 1,000 text messages were entered as evidence by the prosecution. In one message the defendant said he wanted to “move on to the next stage”, reported news agencies.
“You abused the confidence of a child who adulated you,” the judge told the defendant.
The clown intends to appeal.