So, finding old contacts:
Start with what you do know and build from there. If you kept up with just one or two people, ask them if they kept up with anyone else. Then connect with those people, and ask them if they kept up with anyone else.
Use LinkedIn. The search feature is very good for finding people, and once you've found one old contact, it is likely they are in contact with other people from your past. Plus, LinkedIn will even suggest people you might already know, and it is generally pretty accurate in its suggestions. LinkedIn Groups is also a good way to reconnect, as many former employees (and employers) have set up "alumni groups" to help people reconnect with former co-workers.
Search the web. I've found a lot of old connections by just using Google. You don't often get an e-mail or phone number that way, but it is at least a start.
Finding new contacts:
First off, you know more people than you think you do. When you are assembling your list of "everyone you know," don't ignore the butcher, the baker, and the candlestick maker. They meet a wide cross-section of people in the community, so they might well be able to help you in some surprising ways. I've heard story after story of people who got a meeting with a CEO by discovering a seemingly random connection: your barber knows the CEO because the CEO gets a haircut every Wednesday. If you don't mention your need to meet the CEO to your barber, then your barber will not be able to help you.
Get involved. The WSJ article mentions professional associations. Those are excellent groups to join. More importantly, those are excellent groups to volunteer to help. Volunteering your time gets you right in the midst of everything, people get to know you as a doer, and they are more than willing to help you because you have helped them.