This is prestashop module that allows to share cart or order on facebook timeline.
you can give your customers voucher code for such action.
this means that if customer will share their cart or order on facebook - customer will get unique dedicated coupon code
(you can select where module will display the button, in cart, or on order confirmation apge)
more informations about this module you can find on
You can find there only valuable solutions for your e-commerce shop based on PrestaShop engine. Search the best plugin for your store that will meet your requirements and just use it.