How generate thumbnail form video sharing in Facebook

Hello,
My name is Ruben Loureiro and I’m creating a WordPress videoblog.

I’m facing a problem when I try to share videos on facebook from my videoblog, I used the code supplied by the Facebook API to create the like button …. what is happening is that when I press like no thumbnail is generated for the youtube video, a random picture is used from my videoblog.

The link to the video (post) is correct but the thumbnail isn’t it seems to be random, I was expecting a thumbnail generated from the video.

Can someone help me on this issue … I alreday tried to search on google, I’ve tried some tips but nothing worked so far.
I would like to avoid plugins but if you know some working plugins please tell me.

Thank you in advance,
Ruben Loureiro.