That was exactly what happend to the German clones from the so called "VZ" group. The where designed after facebook, but before its internationalisation.

Once FB gained traction here, it was a lost fight for the VZs. The other local social networks suffered as well.

But here the next big thing for the kids/youth is Instagram. So the stay with FB. But listening to them when I commute, it really is, "Have you seen thet thing on Instagram..." when one year back it was "... seen oon FB..."