storereferrals

<a href="https://www.storereferrals.com" rel="nofollow ugc">Store Referrals</a> allows you to create, manage, and track multiple campaigns with tiered rewards. This plugin will track all referred traffic and then update your dashboard analytics in real time. Also, you can optionally display a small prompt for customers to join your referral program after checkout.
<ul>
<li>Create unlimited campaigns with tiered rewards.</li>
<li>Set how many clicks and conversions are required to earn each reward.</li>
<li>Add sample social media posts for your referrers to use when promoting your store.</li>
<li>Easily recruit your customers to join to your campaigns.</li>
<li>Export lists of referrers who have qualified for rewards.</li>
<li>Get real time analytics of how many clicks, conversions, revenue, and referrer sign ups your campaigns have generated.</li>
</ul>

Store Referrals for WooCommerce

Store Referrals is a new kind of referral program that lets you spread awareness of your store using tiered rewards.

wplift

Super Refer A Friend is plugin which adds a new widget to your blog which allows readers to email the page they are on to a friend via a popup box. 
They can enter more than one email address and customise the message that is sent. 
The plugin includes a captcha and you can set a mailing limit to prevent spam
Support at http://wplift.com/refer-a-friend-wordpress-plugin

Super Refer A Friend

Creates a widget to send the current page to a friend via email with a message.

Store Referrals for WooCommerce vs Super Refer A Friend