Now, check out this network graph of the tweets:
The initial tweets that came out came from seemingly disconnected youth living in Midwestern and Southern towns who frequently refer to Christian values in their bios. In other words, these tweets appear to be coming from communities that Invisible Children had already activated prior to launching Kony 2012. Not only did they then each turn on, but they spread the messages to their friends. This allowed the conversation to "pop" and then spread. The one profile that does have a lot of cluster is the Invisible Children profile, highlighting how their audience was indeed ready to respond to them. But you also see tight clusters that were geographically disparate, which bridged from the organization and then spread in their local community with a level of intense density. With this kind of graph structure, it's not surprising that it quickly became a trending topic on Twitter. And then, it could easily spread. Attention begets attention.
Read Danah Boyd's analysis of how Invisible Children strategized their online campaign here: