Facebook has a really cool feature, based on your opt-in email list, called Custom Audiences. Advertise directly to them in their facebook newsfeed, which can be more powerful than an email in their inbox. Expand your audience based on their common characteristics if you have more than 1,000 emails or phone numbers in your list.
We use NationBuilder and facebook together for this purpose. Build your opt-in list in the NationBuilder database. Your awesome magnetic content draws visitors to the website, and they are compelled to sign up for your newsletter and join your movement.
Get the details directly from facebook in this article.