from your analytics software you can track the referrer. if you use google analytics, you can create a funnel and check your conversions. but this wont be too accurate. if you know how to code you can check the referrer on your code and follow them to conversion and keep track of it.
In finance, rate of return (ROR), also known as return on investment (ROI), rate of profit or sometimes just return, is the ratio of money gained or lost (whether realized or unrealized) on an investment relative to the amount of money invested. The amount of money gained or lost may be referred to as interest, profit/loss, gain/loss, or net income/loss. The money invested may be referred to as the asset, capital, principal, or the cost basis of the investment. ROI is usually expressed as a percentage.
I uses google analytics to track visitors from facebook. For ex: i have posted links on www.facebook.com/expertseoservice and the visitors from there that page are showing in my Google analytics account.