I was big on using digg until the v4.0 fiasco a year or two ago, when people started leaving in droves. I switched to reddit and, apart from visiting a couple times out of morbid curiosity, I haven't looked back.
Actually it wasn't killed by Google, Twitter or Facebook. Google is search engine, the others are social networks, though they can spread news pretty fast (especially Twitter) and same is true about Google+. The true reason of Digg's death is the similar (social news sites?), but simpler Reddit, which right now has grown to far more than Digg was (like communities instead of simple content submit). Forbes has already an informative article on that. [I wrote it just because I saw the... tombstone pic]
As for a list of sites look here. It's a number of similar sites. But, in case of tech news, I like the (kinda old) Slashdot. And if you only want news, without the social news thing, you can use the known social networks (G+,Fb,Twitter,...), by subscripting to news pages/profiles.
I never used Digg myself. I can do a little research to find something similar.