Perhaps nothing is as effective and efficient in spreading your message as a viral marketing campaign. The idea behind viral marketing is to inspire people to spread your message for you. It’s been estimated that a successful viral campaign can have 500-1000 times more impact than a non-viral campaign. Boosted by Paid Ads can create the k-factor you always wanted. Thus, to pay for one click and get multiple of them.
All viral concepts should be interconnected and in parallel their message to be clear and not confusing for their audience.
A referral campaign may use all the existing channels and touchpoints of the client e.g. Welcome emails, order confirmation emails, etc.