BuzzSumo - BuzzSumo allows you to discover the most shared links and key influencers for any topic. It's free to use and you can run a search in seconds!

Facebook for Business - Facebook Business gives the latest news, advertising tips, best practices and case studies to meet the business goals.

FameBit - Easiest Way to Find, Hire, and Work with YouTube Influencers

SocialPilot - SocialPilot is an app designed to help businesses and professionals with social media marketing.

themidgame - Connecting brands with influencers (YC15)

Buzzstream - Build Relationships. Build Buzz. Web-based software that helps the world’s best marketers promote their products, services and content.