It sounds like the field you're interested in is web annotation [1].
Genius [2] is one option. Note that all annotations are public, not just visible to your friends, and also that they can be changed and edited by moderators, etc. Here's what a news article looks like with annotations:
Genius [2] is one option. Note that all annotations are public, not just visible to your friends, and also that they can be changed and edited by moderators, etc. Here's what a news article looks like with annotations:
http://genius.it/8344534/www.theverge.com/2015/12/7/9861372/...
Hypothesis [3] is another worth looking into.
1: https://en.wikipedia.org/wiki/Web_annotation
2: http://genius.com/web-annotator
3: https://hypothes.is