Text yes, it might be useful in certain circumstances. Easy to do; expand the existing system for people with speaking difficulties.
Social media? Don't be daft! I don't want my call for help "mediated" by a content-free ad network that might decide to send an ad for Farmville instead. i want the medssage delivered, immediately, and not through Utah or somewhere.
Dear 12yo: if you need help call 112. That's what they're there for.
Here's a question... why don't we teach people to use text in a major incident* like a bombing? It's much more likely to get through than a voice call.
* bearing in mind that the network will probably either be damaged, throttled for Plod, or overloaded.