How to launch successful viral marketing campaigns? What are the factors to take into consideration that are different from the traditional marketing?

Viral marketing is loosely defined as piece of content generated by a person or company that viewers are eager to share with their friends, colleagues, and family members.
It's also defined by its high risks and high rewards.
In other words, most campaigns fall flat on their face, but the ones that succeed reap huge rewards.
Still, that hasn't stopped scores of small businesses and start-ups looking to create the next big hit.
When launching an attempt at virality, remember: No one cares about your product.
As with any advertising campaign, you'll want to be able to measure the relative success of the content.
The first, and most obvious, is to set a benchmark of how many people have actually seen the content, tweeted about it, blogged it, or e-mailed it.
These are all quantifiable variables that your firm can track as soon as the campaign goes live.
Still, there's more your firm can do.
Create content for the right medium.
  When you're trying to make content that will be likely to go viral, especially YouTube videos, you'll want to create content that's been optimized for the viewer to make it easy for him or her to watch and share with family and friends.

There are no right and wrong when you are designing a marketing campaign, you need to understand where you target audience are, which on-line platforms they use and focus on engaging the audience, If you manage to create a campaign where you get your audience to be part of shaping the story, similar to YouTube Viral Video- Harlem Shake, or LAYS campaign to choose the flavour where audience where able to suggest new flavours for potatoes chips.
The difference between the traditional marketing and online marketing can be summarised in the difference in market mix have changed from the 4P's to the concept of 4E's: Product= Experience Price= Exchange Place= Every place Promotion= Evangelism Therefore to be able to design a successful viral marketing campaign that can actually become viral, you need to focus on engaging your audience and turn them into brand Evangelists