backed into by brothers neighbor and now radiator is leaking

my car was backed into by my brothers neighbor with his trailer. we were driving down his street and he had stopped his car, and then proceded to back up before i had a chance to put my car in reverse and start to back up. we didnt exchange information cause there was no visual damage but then a week later my car starts over heating and my radiator begins to leak. i took a picture of his license plate and have his address and phone number. what should i do?