Qld police hunt for teen's attacker

Queensland police are searching for a man they say held a teenager in a headlock and punched him repeatedly in Brisbane's inner city.

One person is already in custody charged with assaulting a 19-year-old man who was knocked unconscious after trying to break up a fight at a taxi rank in Fortitude Valley about 2am on Thursday.

"Police are looking for public assistance to try and identify a second male who was involved," Acting Superintendent Peter Aitken told reporters on Thursday.