There's a Dutch saying that roughly translates to: "Life is a party but you've got to hang your own balloons." Twitter can be a fantastic place for community if you know where to look or are willing to organize it yourself. Tweetchats are a great example of this [1], the phenomenon known as "Black Twitter" [2] is another. (Although many ostensible members of "Black Twitter" have legitimate issues with how "it" is being studied and reported.)[3]
Not to mention the ad hoc communities that spring up around events and pop culture happenings. As with many other things, it might just be a matter of what one makes it.