Had it happen to me, parked my car and returned to it damaged. A witness approached me and gave me the car reg, I reported it to the police explaining all I wanted was my car repaired.
The feds sorted it out, once they contacted the driver, they admitted it and gave a lame excuse for driving off. I got my car fixed and nothing happened to them.
If I seen it I would report it to the person whose car has been hit, let them take whatever action they felt was right.