Google analytics - tracking "social engagement"

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This the code I am using below, however it doesn’t seem to track “social engagement”. Does anyone know how to add code to track social engagement?

Thanks

<!-- Google Analytics Social Button Tracking -->
  <script src="ga_social_tracking.js"></script>

  <!-- Facebook async loading of JSAPI -->
  <div id="fb-root"></div>
  <script>
    // Facebook async loading.
    (function() {
      var e = document.createElement('script'); e.async = true;
      e.src = document.location.protocol +
        '//connect.facebook.net/en_US/all.js';
      document.getElementById('fb-root').appendChild(e);
    }());

    window.fbAsyncInit = function() {
      FB.init({appId: '164838206912600', status: true, cookie: true,
               xfbml: true});

      _ga.trackFacebook();
    };

  </script>
  
    <!-- Load Twitter JS-API asynchronously -->
  <script>
    (function(){
      var twitterWidgets = document.createElement('script');
      twitterWidgets.type = 'text/javascript';
      twitterWidgets.async = true;
      twitterWidgets.src = 'http://platform.twitter.com/widgets.js';

      // Setup a callback to track once the script loads.
      twitterWidgets.onload = _ga.trackTwitter;

      document.getElementsByTagName('head')[0].appendChild(twitterWidgets);
    })();
  </script>