Thumbnails

Hey guys, for some reason, whenever I post something from my blog ( lovexlife.com ) on Facebook it chooses when to show a thumbnail, sometimes it does and sometimes it doesn’t. I have the video thumbnail plugin installed and set featured images, but for some odd reason once every 3 or 4 posts it doesnt show a thumbnail. It gets very annoying, I also used this tutorial to in efforts to help my blog show thumbnails

http://wordpressapi.com/2011/04/13/how-to-add-post-thumbnail-on-home-page-in-wordpress/

Does anyone have any clue on what im doing wrong.

Thanks