Hitchhicking is a possibility. Your best chances are propably going for trucks on petrol stations on the motorway (autobahn). Bear in mind that stopping or pedestrian traffic is prohibited on these, i.e. no one will stop there. Another possibility would be sharing a car with other people. Have a look in the net under "mitfahr". This link makes a decent first impression. http://www.campuschances.de/staticpages/index.php?page=Mitfa hrer-gesucht
good luck