Hi Juan,
Firstly, to recover the post configuration in your sitemap, look at this blog
http://www.hellokg.com/2013/12/15/using-the-default-sitemap-for-dynamics-crm-2013/
The social pane that you used to see on post enabled entities has been deprecated in favour of the new social pane. When you upgrade from crm2011 to 2013, your forms will not have this new social pane enabled. In order to use this with posts, you have to
perform further upgrade steps to re-create your form(s) in the new style. Take a look at this post for a little more information on the process
http://msdynamicscrmblog.wordpress.com/2013/11/08/merge-forms-in-dynamics-crm-2013/
Once you have a new form, adding a 'notes' control will cause the social pane to appear, and will look like this;

Rob
MCTS. GAP Consulting Ltd. Microsoft Community Contributor Award 2011 & 2013