They believe the man who raced down the Ulm-Stuttgart motorway for three km (two miles) before he stopped and fled was a professional stuntman, Goeppingen police spokesman Uli Stoeckle said.
A video of the skateboarder, broadcast on German television networks on Wednesday, showed a helmeted figure wearing a red and white protective suit building up speed by holding onto the back of a motorcycle before letting go and freewheeling.
"We put out an all-points bulletin and have received information that gives us useful clues to who the man may be," Stoeckle said. "We are particularly concerned about copycats who may imitate the stunt, putting their lives at risk."
The film clips show several cars escorting the skateboarder, enabling his collaborators to record the event. The clips have since surfaced on Internet websites.
The German magazine Stern said the mystery man is known in skateboarding circles as a professional stuntman and takes part in international downhill skateboarding competitions.
Stoeckle said the man faces charges for interfering with traffic safety and endangering motorists, and would lose his driver's license and face a "substantial fine." He denied media reports the skateboarder would face a one-year jail sentence.
There are no speed limits on German motorways but there are restrictions on many sections, especially steep and dangerous stretches. The section the skateboarder was using has an 80 km an hour (50 mph) speed limit.