Getting thumbnails on shares

Hi
I’ve installed the plugin and got it up and running showing the like button using Open Graph on all blog posts.
I’d like to know, if there is something I have to do to include a thumbnail from the post includeded with the share comment? At the moment, the space reserved for a thumbnail is just blank.

Thanks for an otherwise great plugin!

https://www.ads-software.com/extend/plugins/facebook-share-new/