Invite Drupal Module encourages the current users to invite their colleges, friends and family members to join your group on social media site. This module work with the User Relationship module.
User Points Module
User Points Module allows users to accumulate points for actions like posting nodes, moderating, sharing a picture, commenting and more. The Drupal site administrator can use these points to upgrade or exchange roles for goods or incentives on your website.
Flag Module works with the Flag Friend submodule. Using the Flag API, Flag friend provides a single or two-way relation type that can share messages and notification to the recipient of the friend request providing information on accepting the request.
This module can be used to display the user activities on the website. Like the Activity Drupal Module, Heartbeat is an API for log activity that can be structured to display in a customized activity stream.
Easy Social is a free social media sharing module which allows you to add a share button on your website. By default, this module includes the widgets for Facebook, Twitter, Google+ and LinkedIn, but you can easily customize it and can add other social media websites.
Activity Stream Module
This Drupal module allows you to create a live stream using your activities on different social media websites like Facebook, YouTube, Twitter, Stumble upon and more. You can easily integrate this Drupal module with any of the websites that publish RSS feeds which provide you the ability for further customization.