Keywords — Check the article for keywords. There might be synonyms for your keyword(s) or phrase that researchers use. There might be additional keywords that will help you to narrow the scope of your search. Keywords are usually found above or below the abstract. Redo your search with these other keywords.
References — Look through the article's references. You should be able to find citations to older, relevant articles there.
Authors — Search for articles by the same author(s). The author has likely written other articles on the topic.
Journals — Search the same journal. If a journal has published one article on a topic, it's a good bet that they have published others.
Look for the article you already found in the library's search box, Google Scholar, and Scopus. There should be a link to "Cited by", which will give a list of articles that cited the one you already have — meaning newer articles on the topic that might be relevant.