you must forgot to set related informations in admin panel(social authentication)
Share post content on facebook twitter ..
Each post has an icon to share on social networks - on this forum (using the Persona theme) there's an icon to the far-right of the post with 3 dots stacked on one another. Click it to choose to share on Facebook, Twitter of G+.
On Lavender theme there's a cog button under a post which when clicked offers the same options.