Can a towing company auction a vehicle without notifying its registered owner?

only if they have a lien on the the title for any service that you have not paid for. its called a mechanics lien.
Even if they have a mechanics lien, they still have to notify the registered owner via certified mail, and give them a chance to pay the bill. You can't just get a title or magistrate's bill of sale without proof that you have done everything possible to contact the owner first. The owner has 30 days to contact the person that has the vehicle. If they don't, then the vehicle can be sold at a magistrates auction and will be given a title for the vehicle.