It's one thing to track success with an immediate call to action, but if your call to action wasn't your "end-game" for a customer then it's important to invest in an analytics solution that allows you to track your customers through multiple calls to action all the way through a sales funnel.

MixPanel and KissMetrics are both excellent tools that allow you to create a sales funnel and track customers from source, call to action, engagement, through to their purchase and referral stage.