How you can meaure ROI of Social Media Marketing? what are the important KPI's?

ROI is very hot topic in marketing in general!! To measure ROI you need to set your objectives first or KPIs then you can measure if you achieved it or not.
In Social media the main KPIs is reach, engagements, and action.
for reach, how many of your target audience you reached by your social media activities, and how they are engaged with you activities (share, comments, likes, retweet, subscribe,....) and finally if you have call to action is it achieved or not.
Finally, to measure ROI in digital you need to ask yourself the following questions
1- How much are you ready to pay to acquire one new customer?
2- How worth a new customer to my business?
3- What is the action required from customer to achieve your objectives

Set the following KPIs Fan base Engagement Rate Leads generated via contest Traffic to webiste Sales (usually not much via social media) RT for your tweet Run promotions and see how much conversion you are getting Regards, Somesh