A coworker stole from me and I proved it to my boss but there was minimal to no punishment... is there a law against this?

I assume that your boss did not feel your "proof" actually proved your accusation. If you feel that any law has been broken talk to the police.

No. Unfair is not illegal.

It is not your employer's job to punish people for stealing. That is for the police to do.

Report it to the police, and take the thief to civil court to get your stuff back.

The boss isn't the law, dear. They don't have to punish anyone.

Yes. It is called theft. You can report it to the police if you want to. You can also sue him for the value of the item.

yes and thats why i wouldve told the police about it instead

There is a law against stealing. I'm not sure if that's what you meant.

Your boss is not the police. It's up to him how to handle it.

There are laws against theft of personal property. Usually you get the police involved in criminal matters.