I have two checking accounts, one is joint in mine and my husband name that other is just in my name. The collector has put a freez on the account that is just in my name, can they also put a freeze on the joint account as well? Also, How do collector find out where you have an account with?

Yes they can put a freeze on any account that you hold jointly with anyone else. There are a variety of ways that can be used to find out what bank accounts you have.