There is nothing worse than finding out that someone has stolen your article from your blog or website and not given you credit where credit is due!
Alot of people rant on about copyscape, I find copyscape is a good website and does its purpose but I find it only shows you the first 5 websites that have your content and you have to pay for anything else.
Check this out
Plagiarism Checker
I have been using it for a couple of years now and I have caught 2 website owners that have stolen my article and manage to have the article removed from the "webmasters" website.
Let me know how you got on with it.