Building a community from the ground up takes a lot of work. To make your community more popular with your visitors, you need to provide them with tools they can use to bring more people to your website. WP Social Invitations happens to be a useful plugin that allows your visitors to invite their friends into your community. It supports social networks such as Facebook, Twitter, and Foursquare.
This is a freemium plugin. You can add your social media information, customize message templates, change e-mail settings, and style the widget. The premium version is much more powerful though. You will be able to lock your content and make it available to those who were invited by their friends. The plugin is compatible with Invite Anyone.
The pro version of WP Social Invitations offers integration with MyCRED and Cubepoints. It also offers Gmail and SMTP support. It works on private sites too. The plugin has filters and hooks for developers and can be updated like regular WordPress plugins. WP Social Invitations costs $20 for a single site at the time of this writing.