Matheus Henrique Marioto jumped into the lake from the south side of a bridge (Quaibrücke) during the Zurich techno party, which attracted almost one million visitors on Saturday.
Marioto had travelled to the city with friends from Germany for what is billed as Switzerland’s biggest street party.
At around 6pm on Saturday he told colleagues he wanted to cool off, city police said on Tuesday.
He took off clothes and gave them to a friend before jumping off the bridge into the lake and swimming away.
His friends were not aware that he had disappeared until it came time for them to meet up to return to Germany and they realized he wasn’t there, police said in a news release.
The friends subsequently contacted police to report his disappearance.
Since Saturday police boat patrols with divers have searched the lake and checks have been made of the Limmat River, which flows out of Lake Zurich.
Zurich police described Marioto as a slim man 165 centimetres tall with short brown hair.
Last seen wearing only shorts, he speaks Portuguese and broken German.
Police are asking anyone who may have information about his whereabouts to phone 044 411 7117 or to contact any Zurich police station.