Thumbnails

I recently moved my site from wordpress.com, and an issue I’ve run into is that when I share an link on Facebook, the thumbnail is blank or my logo. There also isn’t a thumbnail when I look on google. I haven’t tried sharing other places, but I do use Facebook to share links a lot, so it would be great to have the correct images.
I’ve tried using Yoast to set my thumbnail to the image I want (no luck, plus I would rather not have to go through and change each manually). Any thoughts?

The page I need help with: [log in to see the link]