There are three main platforms I use, Facebook, Twitter and Google+. Each has its relative merits and issues, and each allows me to connect with different online communities, although there is always an amount of crossover.
I really only use Facebook to communicate with New Zealand Science teachers in one group and NZ Biology teachers in another, although I do also use the NZQA forum, specifically for updates and moderator's comments. Facebook tends to usually be my more private social medium. These are really useful, closed communities which allow discussion topics and issues, sharing ideas (and assessment tasks) and posting interesting articles.
Google+ has been a steady place for growing my networks for several years now. Mostly, I connect with communities about Google products and education, but it has never caught on as quickly as some of the other platforms. There are a lot of Google product forums, as well as the MindLab communities, which I do use relatively frequently (OK, I use the MindLab one mostly, currently, and I have neglected some of my other communities while doing this Post Grad).
For speedy, bite-sized chunks of information, Twitter has all manner of useful conversations, often with their own hashtag making them easy to follow if one is using a social media management tool (I use Hootsuite) as the hashtag can be saved as a separate stream, thus filtering out the waffle (there are no, or very few posts on Trump in the education streams...)
What Twitter lacks in amount of characters available (140 characters) it makes up for in the types of connections that a busy teacher can make, allowing access to educators around the globe who share my interests. It is a great place to get an answer to a question or to find something new that someone else is trying, to connect with like-minded people discussing an educational topic, or even to follow what is happening at a conference such as uLearn when you don't attend in person, as discussed by Melhuish (2013).
Where else can you get all of this (free) PD? Yes, it takes some practice to find and interact with the right people, but it is time well spent. There are hashtag conversations on #edchatnz and #scichatnz, places where the conversations are people you run into face to face at conferences and summits (although in some cases it almost amounts to meeting a 'hero' when you meet them for real, I have heard "I follow you on Twitter" more than once!)
The really big deal for me is the generosity and collaborative nature of the networks I have joined. I can get advice from secondary and primary teachers, scientists, people who can help me transform my practice, despite the sometimes overwhelming amount of information out there.
In modern education, we should make sure we are not working alone. The days of clusters where only three people attend, and two of them are there for whatever resources you can provide them with, are nearing an end. I actually can't remember the last time I even went to one of these clusters. Now, when I want to know how to do something neat or learn how to use a tool like OneNote Class Notebook, I turn to my Tweeting colleagues for advice (with thanks to @ibpossum for this last one!)
No teacher should be working alone anymore, even if your colleagues are in a different country and teach a different subject to you, get out and get social.
Melhuish, K.(2013). Online social networking and its impact on New Zealand educators’ professional learning. Master Thesis. The University of Waikato. Retrived on 05 May, 2015 from http://researchcommons.waikato.ac.nz/bitstream/han.