I spoke today at the Central Valley Professionals, a job club, about networking to find a job. It's too late to start building a network when you begin a job search. You really need to rely on the people you already know. Along the way, you can strengthen your existing network and even grow it so the next time you're looking for a job it will be much easier.
I encouraged them to get back in touch with people they haven't spoken to in a while. These are some of your "weak ties" - co-workers from a past job, old friends, fellow alumni, people from a club you used to be in - people you once had a fairly strong relationship with, but are somewhat out of touch.
Is it ingenuous to suggest that you get back in touch with these people without motive? But still looking for help that they might be able to offer in your job search? Maybe it's the excuse you need to call them. If you imagine that they would be glad to hear from you again, why not have something concrete to call about?
It is important though, that you make sure to keep the relationship going after you get a job. If you called them just to get something from them without intending to rebuild your relationship then your insincerity will be worse than never having called them at all.