I think a Facebook competitor's critical mass problem is much harder than then a competitor to Reddit or Twitter's. The appeal to Facebook is that you have all the people you know on there, and you can share updates with the mall and see updates from them all. As the portion of your friends and loved ones drops, it's utility drops proportionally. If everyone uses Facebook, it's a great tool; but if only 10% of your friends do, it's kind of worthless. You don't really want to have to post photos to two or three different sites to really share them. Having one place to connect with everyone in your life is kind of the point of Facebook.
On the other hand, Reddit and Twitter are just random things shared from random people. If you randomly deleted half of Reddit users or Twitter users, I literally wouldn't even notice. There about the containt comma you really don't care about or even really know the actual people.
I think a Facebook competitor's critical mass problem is much harder than then a competitor to Reddit or Twitter's. The appeal to Facebook is that you have all the people you know on there, and you can share updates with the mall and see updates from them all. As the portion of your friends and loved ones drops, it's utility drops proportionally. If everyone uses Facebook, it's a great tool; but if only 10% of your friends do, it's kind of worthless. You don't really want to have to post photos to two or three different sites to really share them. Having one place to connect with everyone in your life is kind of the point of Facebook.
On the other hand, Reddit and Twitter are just random things shared from random people. If you randomly deleted half of Reddit users or Twitter users, I literally wouldn't even notice. There about the containt comma you really don't care about or even really know the actual people.