Virality is not a feature you can add after designing your product. It is neither adding “Like” or “Tweet this button” nor vigorously integrating all the Facebook Social Graph API features. It is instead something inherently built into your product.
Are you about to launch or have just recently released your freshly built web service or mobile application? There are many ways to get noticed and acquire your first customers. It is always easy to pay for clicks on Google, Bing or Facebook. But with only a little time and effort and without investing any money, you can generate remarkable reach within your target customer group.