You have 2 options really.
If it is parked in or on private land and you have no parking permit on display, you can contact the police and request a Grua to remove the vehicle immediately.
If you do not have a no parking permit, you must contact the Police ad tell them of an abandoned car. They will come and put a removal pending sticker on it, giving a specified time for the owner to remove it. After the period of time is up they will send a Grua and remove the vehicle.