I don't think any of them failed, they were all relevant for a period of time, and users moved to a different network. That is happening with Facebook, will happen with Instagram, and is just part of the cycle.
Bebo founder is selling his house in SF for $39 million [1], that doesn't seem like a failure to me.
[1] https://www.wsj.com/articles/tech-couple-list-their-eclectic...