It took some backtracking, but I think what the Telegraph article was referring to was this: http://blogs.ucl.ac.uk/social-networking/2013/11/24/what-will-we-learn-from-the-fall-of-facebook/
For starters, unless I'm mistaken about which article they're talking about, the study wasn't conducted in 8 countries, but one: namely, the UK.
I don't know about the rest of the world, but in the small bubble where I live, my friends and I still regularly use Facebook as a means of interaction (I'm currently 16). Sure, we also use Instagram and Tumblr and Snapchat - those are all there (but for the life of me I have yet to figure out why Snapchat is as popular as it is...). But Facebook is still the primary method of chatting, sharing information, posting pictures, whatever. And yeah, we have Twitter accounts, but Twitter is more for public broadcasting, whereas Facebook has the ability for targeted posting... kind of. In any case, I wouldn't say Facebook is DEAD. My friends all across the country (US) do say that they use Facebook more than other methods of communication out of sheer ease of use.