Harnessing these new technologies
to create and grow our own PLNs is imperative for educators who want to stay connected to the changing world we are charged with introducing to our students.”

Personal Learning Networks enable teachers and student teachers access to a wide range of experts and communities to support their professional learning. This can be facilitated through the use of a range of ICT tools, some of which include professional learning communities and websites, social networking sites (Facebook, Twitter, LinkedIn), social bookmarking tools (Diigo, Delicious), wikis (wetpaint, Wikispaces) and MOOCs (Massive Open Online Course).

Essentially, anyone that you interact with, whether they are social contacts, professional peers or experts in their field, can be considered part of your Personal Learning Network.
Warlick goes on to describe three main types of PLNs:

Personally maintained synchronous connections. This is the traditional network that includes the people and places you consult to answer questions, solve problems and accomplish goals. Today, however, you can enhance this PLN with new tools such as chat, instant and text messaging, teleconferencing (using iChat, Skype, uStream), Twitter, and virtual worlds such as Second Life.