Hicham,
Our upcoming 4.3 release (late this month, if all goes well) will have Open Graph Action abilities built in for things like reading articles as well as an easy way to add actions for other events. For more information on the upcoming release, please see our
SourceCoast Roadmap to Joomla 3.0
blog post.
If you have, or are, a developer, I can point you to some threads where we've helped users implement actions in the past. However, it can take a bit of work, just to warn you. We can help with the Facebook calls you'll need to make, but understanding where to make changes to Joomla's content component and things like that will be things you need to investigate.
Just let us know and we can point you in the right direction, or just wait a few weeks, and hopefully the next release will have what you need!
Thanks,
Alex