Looking for social networks and forums for businesses

Hey, I'm researching a list of forums and social networking sites to grow my IT solutions business presence.

Currently I have:
quora.com
linkedin.com
inbound.org
medium.com

twitter.com
facebook.com
pinterest.com
https://plus.google.com/
(instagram and tumblr)

For forums I'm really undecided. Only have WarriorForum and DigitalPoint on the mind.

So maybe you could help out and tell more social networks/forums which can be used?