Viral Marketing of a website / Facebook application / users engagement

Hi everyone we have an e-commerce website buying and selling would like to advertise our website in a way people can interest in and can share and recommend with their friends and family. Means viral marketing and engagement. 1. What application or strategy you will develop or create to get users. 2. how the users will keep coming on the site and keep recommending Please give your feedback as well as suggestions how we should engage visitors into more activity on the website. We will assign the project to the only company / person who will add more value in the application to make is social and viral. Any samples or examples even on 3rd party websites will be encouraged to share with us.