From time to time there are articles claiming the end of Facebook. These articles are all pretty much the same, saying how "kids" are using other social media sites now, such as Vine, Snapchat, Ask.fm, and Instagram. Really?
Vine is not used instead of Facebook. Vine is used instead of Youtube. It's a video app.
Snapchat is only being used for sending sexy videos that cannot be stored. Again, not something that was ever really Facebook's thing. Facebook might be losing some use to Snapchat, but I don't think it's much. Youtube is losing more than Facebook.
Ask.fm is really competition for Reddit and Yahoo! Answers rather than Facebook. Maybe Reddit is stealing time away from Facebook, but ultimately, even these individuals end up on Facebook for social networking (even as they pretend to hate it). Reddit doesn't have a strong social interaction and is mostly just strangers posting for strangers.
What about Instagram? People use Instagram instead of older services like Flickr and Photobucket. It's a photo app. There is a stronger social aspect, but photos aren't really a replacement for communicating on Facebook. It's more like one-way bragging, which ultimately doesn't promote long and engaging interaction. When people respond to someone else's brags, they are trying to make themselves relevant in the context of the braggartry, and that's what tends to happen on Facebook. That's something that just isn't possible on Instagram.
You know what kids are using instead of Facebook? Nothing, ...kinda. They are using text messaging. Texting is why Facebook is seeing a small decline in usage in the younger demographics. Aggressive use of texting is temporary for people, though. Textings doesn't grow as your network grows. There's a certain point where texting becomes intrusive. When that happens, people move their social networking to a more broad service. When they do, that service still tends to be Facebook.
I'm not a Facebook pumper. I can live with or without it. I do know it is the most convenient service right now. There is just something about it that makes it more usable than Google+. Anyone that thinks that Facebook will go the way of Myspace and Friendster just isn't paying attention or only seeing what they want to see. Until something that is actually better comes around, Facebook isn't going to die from a supposed mass migration of its user base.
There is merit to all the services mentioned above. Some services appeal to certain people more than others. Facebook's success is that it is a generalist that covers all the bases.