You mention social network, I think it is also critical to build up a good professional network. The group I am part of has a couple of individuals in their 50s, one a specialist and one more of a generalist. They joined the company through professional connections they had worked with before.

I'm purposefully making a distinction between "a random set of contacts" and a more targeted group of people who you have worked with, know your strengths, and want to work with you again.