Ugh....Why do people steal other peoples work?
Most of the thieves see absolutely nothing wrong with stealing your work, so talking to them is almost always a waste of time. It's best to contact the company which hosts the thief's site. Sometimes you get lucky and are able to get their site shut down. Unfortunately, most of the time you have to live with it.
On your end, all you can do is make sure you have a legal copyright notice in the code, and include some wording which states how/if your code can be distributed.