Here are a few sites that I use to help with promoting and growing my customer base for the eBay store that I run as well as other social media sites.
https://twuffer.com/ – Great site that lets you schedule Twitter posts.
http://sproutsocial.com – This is a one stop content management tool for all your social media sites. Very easy to use and a great tool!
https://ritetag.com – This site will look over and compare your #hashtags that you use in your posts and provide statistics and suggestions.
https://statusbrew.com – Another great tool to schedule posts across multiple sites.
https://moz.com – Site that will be able to tell you who your followers are, location, demographics, etc. Great way to build a database on who you are attracting and not attracting to your site.