If you wrote the article as a part of your work, it is likely that you will be deemed to have assigned certain rights to your boss. If you wrote it outside of what would be considered your job, then you have retained full copyright.
In a recent briefing about copyright, we were told that the best you can do is write to the person and ask them to remove it, since they are infringing your copyright. If you really want, you can back this up with a legal letter, but this will cost a reasonable amount which you will not be able to recoup. If you believe they are exploiting your copyright to make money, you have a right to that money. Regardless, once you have made them aware of your copyright, they are subsequently liable for any exploitation that occurs. Don't forget, any legal action is liable to be expensive and probably not worth it. You also need to check whether the magazine to which you submitted the article had a clause in which you volunteered to give up your copyright.