Depends on the industry. Though Facebook/LinkedIn are very valuable tools to make that first warm contact. But don't depend on them. The key is to use a combination of online and offline tools. So, introduce yourself on LinkedIn, have a nice email chat, then meet on a Skype/phone call. When you are done, send them a nice card through regular mail.
After not being able to find the phone number for a large audio visual company, an admin I worked with searched for the company name using Google Maps and found both the 800 and local phone numbers.
Online intros via sites like linkedin are much more in vogue.