The skater can be seen on video-sharing website YouTube hanging onto a motorbike to get up to speed before letting go and whizzing downhill along a motorway in southern Germany.
German autobahns often have no speed restrictions but the picturesque stretch of road concerned outside Göppingen near Stuttgart has a limit of 80 kilometres per hour.
According to press reports the man, dressed in the video in a red and black jumpsuit and an aerodynamic white helmet, is a stuntman and well-known international downhill skater. A comment on YouTube suggested he was Canadian.
But police were not amused, with spokesman Uli Stoeckle telling AFP on Wednesday they were trying to find the skater and that he was being investigated for dangerous behaviour.