Linkedin is the only social network specifically for business to business networking. You write a profile for yourself, can post updates and have a news feed much like Facebook. It's key differences are:
Linkedin has over 450 Million users with a male bias (>56%).
Joining, contributing to and/or creating Linkedin groups that are relevant to your sphere of expertise is a good way to raise your profile. You can pay to message Linkedin members that fit chosen criteria.
Linkedin is heavily used by recruitment consultants and marketeers who will ask to connect with you in order to promote themselves, choose your connections wisely if you want to avoid spam.