Citation chaining (also called reference chaining or reference mining) is another way to expand your search. It involves reviewing the reference lists of a key article you have identified in your search. This is referred to as backward chaining. You are looking back at the citations that were relevant when that key article was written (looking backward). To perform this task, you review the reference list or works cited in the paper. 

You can also do forward chaining. Forward chaining involves looking at the sources that have cited the key article to identify more recent material covering similar topics. You are looking what was written after the key article was written (looking forward). You can do this in Google Scholar, PubMed, Web of Science, or other databases. By clicking on the "cited by" in Google Scholar, you will discover more recent articles. 

Be mindful that using citation chaining is one part of the search process and should not be the exclusive method of uncovering additional articles. Also, be aware that you will still need to screen the new citations you uncover to determine if they are relevant to your research question.