Website: http://www.atheistrepublic.com/
Facebook: https://www.facebook.com/AtheistRepublic/
Twitter: https://twitter.com/AtheistRepublic
Atheist Republic is a global atheist network founded by Armin Navabi with loads of valuable resources and articles for Atheists. They make use of a number of platforms to promote atheism and critical thought, they are incredibly vocal group when it comes to advocating against religious propaganda.  They also run a number of volunteer programs if you would like to get involved with their mission.