Online communities like those listed on this page are primarily designed for professionals in various disciplines to network, share their work, engage in informal discussions, or even collaborate on projects.  Note that these communities tend to be more work-focused than those under "social media", although they share many of the same features.  You might choose to customize and curate your profiles on these sites a little differently than your social profiles depending on your purposes.

According to the blog post, How to promote your research through blogging, there are ~77 million new posts each month on WordPress alone. With such a proliferation in online content, blogging (or following blog writers in your discipline) helps improve your content's discoverability and can facilitate a meaningful exchange much faster than traditional methods, like the Pony Express. It also dovetails with the growing trend of content needing to be open, inclusive of non-academic communities (e.g., professional organizations) and various audiences that may not have access to peer-reviewed research journals. 

Many disciplines have their own, specific community or forums where networking and information can be shared. If you know of one not listed here, please send us the link.