The Facebook social sharing component works differently than all of the other social providers.  In order to use the social sharing feature with Facebook, you must first complete the instructions listed in the Facebook Developer App Guide.  In addition, you  have to enable the "publish_actions" permission in Janrain as listed below. 

In Janrain:
  1. Log into
  2. Click on the Manage Engage App icon (the blue word bubbles) next to your Engage App Name
  3. Under the Providers section, hover over Facebook and click on the Manage Permissions icon (wrench icon)
  4. Scroll down to the Social Sharing section and check the box next publish_actions