Facebook offers a great utility for previewing and debugging the way shared articles appear on their platform.
You can use this tool with any Facebook account — it does not require that you own or administrate the Facebook page where the article is being shared. (All changes are actually made on the back-end of the website itself; the Facebook Debugger is used to refresh the way an article appears if changes were made after an article was shared.)
You can access this tool here: https://developers.facebook.com/tools/debug/sharing/
Enter any URL and Facebook will search to see if the URL has been previously shared on Facebook. If so, it will show how the preview looks — title, preview image, etc.
Changing Your Preview Image
You can adjust the image that appears with shared stories in your WordPress Dashboard under the “All In One SEO” plugin. Select the “Social Meta” sub option.
Under the box titled “Home Page Settings” there is a setting to upload an image to be used specifically when sharing the homepage.
Home Image (Upload Image): Upload the image you’d like to use for when the Homepage is shared on Facebook.
Under the box titled “Image Settings” there are several settings that help determine which image to use in which situation.
Select OG:Image Source: “Featured Image” is the default option, which means Facebook will always use the Featured Image as the preview image when an article is shared on Facebook.
Use Default If No Image Found: Check this to tell Facebook to use the “Default Image” (defined below) for articles that do not have a Featured Image set.
Default OG:Image (Upload Image): This allows you to upload a default image to use in place of a preview image for any articles that do not use a Featured Image.