What is a PLN? A PLN is a professional learning network, usually online where a person can go for help, tips, and advice in his or her professional field.
For example, Mr. B Ed Tech (www.mrbwebsite.com) is my PLN where I go to get help, tips, advice, and contribute my experience for other technology and education professionals.
Out of my experience, my favorite tool by far has been Twitter. For those that I know personally or face-to-face, I use facebook, but I also have a Mr. B Ed Tech group on there as well. Pinterest is a great place for teacher resources, but I have not found it helpful to me personally. I do post some things on there, but I rarely find anything on there.
The most helpful to me has been email list-serv(s). This is my first stop for tech issues that puzzle me. I usually post a question and within minutes someone posts back with the solution or a "me too" comment. Those "me too" comments are sometimes a life saver as it lets me know the problem is not just localized to my environment.