Recently, I was trying to add my site to facebook, google plus and Pintest. I have notice that if I just add the link of my site, there's no image display and no description. Also, so here is few help links I think it would help you to develop your site to be more social.
Thanks! This article was very helpful.
Looks like facebook have cache issue, I'm not sure how facebook will refresh it. Eventhough I set the image to my site, it was able to show at Google Plus but not from facebook.