Eliver,
I was sure that I had posted a response to this earlier, but apparently, it's not here..
The button you're using on your page is the Like button, not the Fan/Like-Box. The Like button only will show faces of friends of the current user that is logged in. The Fan/Like-Box widget only works with Facebook Pages, but shows more information like the activity stream, a like button and faces of all users that have Like'd the FB Page. So, the faces may not be showing if you aren't logged into Facebook or if your FB user isn't friends with anyone else who has like'd the FB Page.
It sounds like you may want to try the JFBCFan module instead if you always want faces to show up.
Hope that helps,
Alex