The APA Dictionary of Psychology defines empirical as: "derived from or denoting experimentation or systematic observations as the basis for conclusion or determination, as opposed to speculative, theoretical, or exclusively reason-based approaches" (p. 327).
Therefore, an empirical study is one based on "facts, systematic observation, or experiment, rather than theory or general philosophical principle" (APA Databases Methodology Field Values).
It is easy to find empirical studies in PsycInfo.
On the Advanced Search screen, scroll down to near the bottom of the screen and choose "Empirical Study" from the Methodology limit box:
If you have already done a search, look for the filter for Methodology on the left side of the search results screen: