Here's an example of a search in ERIC to find peer reviewed empirical studies on a topic.
In ERIC or PsycINFO, you can limit your search by publication type or method.
AND for when you need all terms in a search string included in the articles you retrieve.
OR for when you have more than one way to say the same thing.
* ! wild-cards for getting a root word and all of it's endings, for example: communicat* will search for communication, communicating, communicates, communicated, communicator, etc.
The Google Scholar Cited By feature will identify subsequent citations to articles that might be relevant to your research.