South Wales Police said around 50 officers are deployed in the "extensive" search for Ben Thompson, including a helicopter and search dogs.
Chief Inspector Eddie Ough said he believed Ben had left the city centre to try to walk back to where he was staying that night.
He asked people in the west of Cardiff to look in their outbuildings, as "Ben may have tripped, fallen, hurt himself, be unconscious."
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Calming down tonight with clear spells and cooler temperatures! Setting us up for a decent start to the weekend!
Callum Williams of Wrexham pleaded guilty to causing grievous bodily harm to the woman police officer, assault and damaging property.
RSPCA says at first they thought the caller had confused the animal with a badger.