Co-Authors Plus is a plugin built and maintained by Automattic that allows you to define multiple Authors for your content. This extension will index and make searchable all multiple Authors.

Once the extension has been activated, you must rebuild your index on the Advanced tab of the SearchWP settings screen, and then trigger a reindex.

While the index is rebuilding, you’ll notice a number of new Custom Fields in the SearchWP settings dropdown for each post type, they all start with coauthorplus_

By default the extension will index:

• user_nicename
• display_name
• nickname
• first_name
• last_name
• biography

and there are separate entries for each of those, but the extension also bundles all of those fields into a coauthorsplus_any Custom Field if you want to match any of those.

Once the index has rebuilt you will be able to search by Author data as defined by Co-Authors Plus. Searching for configured Author data will return the post(s) written by that author, not the Author archive or a User profile.