If you need a flexible and lightweight social share plugin for joomla you should look at  SP Share  ! This is really an awesome plugin for its features. You will able to share your Joomla or K2 contents with Facebook, Twitter, Digg, Linkend and Plusone followers in a very easy way using this plugin. It allows you to display the share button like a button or box style and can be placed at four different positions in an article.