If it's a book or a chapter in a book, search for the title of the BOOK (not the chapter) in the library catalog.
If it's a journal article, do a title search in this box by switching the pulldown that says "keyword" to "title" and then entering the title of the JOURNAL, not the title of the article.
Once the journal title comes up, enter the TITLE OF YOUR ARTICLE in the box that says "Search within Publication."
Search for your article in Google Scholar. Once you've found the citation for your article, click the link that says "Cited By." at the bottom. The resulting articles are all the ones that have cited your article since it was published.