A viral campaign has a few necessary ingredients to get a viral social success.
One is that it needs to have some value in passing it to my friends. I don’t want to look like I am abusing my friends. I want to be the first one to post the new link and idea. So being cool, or for the social good (like cancer research), will probably get you there.
Then you need permission. Don’t spam or interrupt. Ask permission.
Some smart guy tweeted me this link about 3 successful viral campaigns in social media. 1 & 3 show that permission was important. They all had value to pass on.
I think the asking is an important part. “Please send this to your friends”. Value. Permission.