If Posts tab is not showing in Social Pane, then go to Settings-> Post Configurations tab, as shown in snap shot.
select relevant entity. Now activate/publish entity.This will activate the Posts tab in Social Pane on Entity Form.
If Post Configuration tab is not showing in setings area, then you have to edit the sitemap of CRM. This usually happen due to up-gradation from CRM 2011 to CRM 2013.
Ali Wadood
Dynamics CRM Consultant Maison Consulting & Solutions
