mattdu

This plugin uses the custom taxonomy features of WordPress to create “bylines” — essentially, tags representing authors who contributed to a post. The differentiating feature of this plugin is that it should not require any modifications to your theme files (assuming it is already displaying the post author).
This plugin would be useful for publishing situations where the majority of your content is from contributors who you don’t necessarily want to have access to your back-end. It still conveys the appearance that the authors are members of the site (it provides a built-in archive page for each Byline). If your theme displays tag descriptions, you could use the Byline description field to identify guests vs. “staff” writers or provide other author information.
You can see an example of this plugin at work at http://thedailycougar.com

Byline

The Byline plugin is simple and suitable for multi-author WordPress sites.

Best For Multi Author

Solves the co/multi-author problem without modifying the theme. Uses a custom taxonomy, "Byline," that replaces the Display Author.

Frank Neumann-Staude

Ulf Schönefeld

polyres

This plugin/add-on requires the plugins FacetWP and Co-Authors Plus (WordPress plugin repository)!
This free plugin/add-on integrates FacetWP with Co-Authors Plus, allowing you to use Co-Author Plus custom fields for front-end search and filtering in a facet. 
With the help of Extend Co-Authors Plus for FacetWP, you can create a lable and choose the data source “co-authors” for your page or post.

Byline vs Extend Co-Authors Plus for FacetWP