For some unknown reason, the feacebook like message box displayed at any k2 article shows half size, so we cannot add a comment to a like action. Searching on the k2 forums we found a working solution to fix this problem:

Source: http://getk2.org/community/English-K2-Community/170767-Facebook-LIKE-button-SHOW-HALF-of-the-COMMENT-FORM

1. go to this directory: /components/com_k2/templates/default/item.php (or /templates/your template/html/com_k2/default/item.php)

2. find: "fb.like"

3. Then modify the data-width. I changed mine to "450" for full width facebook comment form

Done!

Este es un artículo creado desde el frontend. Desde el menú de un usuario publisher. Es muy fácil y sencillo.