Hello,
I tested all the social networks in WP socializer and looked about them on Google, here are the social networks that surely don’t exist anymore :
connotea, mob, propeller, ping.fm, posterous, tipd, wikio (it is now only a price comparison website), faves, fleck, grono, scoopeo, sphinx, google reader, identica (now it is pump.io), yahoobuzz (perhaps replaced by flickr ?), internetmedia (redirected toward linkr), laaik.it ((redirected toward 24.com), slashdot (doesn’t accept bookmark creation anymore).
I noticed others websites that doesn’t work but I’m not sure if it is temporaly or not.
You could add facebook in other langages, by exemple :
facebook (français) : https://fr-fr.facebook.com
facebook (deutsch) : https://de-de.facebook.com
facebook (italiano) : https://it-it.facebook.com
etc.
