NationBuilder includes some great tools that allow your supporters to share your website via their social networks. You can read about how to optimize each page on your website for social sharing here: nationbuilder.com/optimizing_your_content_for_social_media
Your custom theme includes an expanded set of page-level sharing tools (we've added options to share by email, Pinterest, Linkedin, StumbleUpon, and Reddit.)
We've also added a feature that allows you to include a "sharebar", which promotes the prewritten tweet that is configured for that particular page at the top of the page. To turn on the sharebar, simply add the tag "sharebar" to that page.