Mendeley

At the top, right corner of the central pane, is a search box which you can use to find references within your own library.

To search your entire library, make sure All References is selected in the left hand menu. If you want to search only those references in a particular collection, select that collection.

• Enter your search terms(s) into the Search box and click on the magnifying glass icon to return references in your library which contain the term(s) in their document details (not the full text of PDF papers). 
• Search acts as a filter, and to display All references again, you will need to remove the filter, by clicking on the 'X' to the right of the search terms (in the Search box).
• If you want to find all references with a particular author or tag, this can be done by clicking on the Filters option in the top, right corner.  Select either Authors or Tags via the two tabs; this will return just the references with the selected author or tag. You can filter further by adding additional author names or tags. Turn off the filter(s) by clicking on the 'X' to the right of the filter or click on Clear filters.