Hi Danilo,
Seems like the video that you've upload from the youtube doesn't have sddefault.jpg format where by default it will using this format so it will not displayed the video image. I've make temporary fix for this in the file:
JoomlaFolder/administrator/components/com_easysocial/includes/crawler/hooks/youtube.php
But it will effected as you upload a new video in the site. For the previous video that have been uploaded in the site we have manually change the format in database. In order to do that, we need your PhpMyAdmin access.
You can add the information needed by edit your first post in the Details section or you can just include your site's access once at
http://stackideas.com/dashboard/site rather than needing to keep adding them in your replies