Things go viral, as you said, purely by happenstance. If we knew how to MAKE them do it then a lot of us who rely on advertising our products and skills would be VERY happy people indeed!
We spend thousands of dollars a year on our posts and ads, just hoping that they'll go viral but even with a lot of money, it doesn't always happen. Unfortunately, there's no guarantee that it would go viral even if a celebrity shared it. What the public wants to see/share/read from one day to the next varies and there's no way to guess what that might be on any given day. And, also unfortunately, there are LOTS of unsolved cases and missing persons out there. I belong to a few FB groups and dozens of stories and links get shared every day. Very difficult to make one stand out from the other, especially since they're all important in their own way. With that being said, getting someone famous "on the case" couldn't hurt. When I saw Nancy Grace again last fall, I mentioned it because I thought that she'd pull through with it and hype the attention, but she's moved on to other things. Someone with a big social media following would be helpful.
In terms of actually "going viral", however, the story technically has. The sketch has been shared more than 20,000 times. That's a lot more than most and the term "viral" just means that it's been shared and passed around a lot. Now, a year later, unless there is some major news or case activity, we're not going to see much more activity than that.
