I know I'll sound elitist but introvert or not this doesn't make any difference, the most important part of your network are the people you've worked with already.

If none of them is pinging you at times to see if you're available, you were probably an unremarkable professional or you have extraordinarily bad luck.

It's not a bad thing to be average or mediocre, it's what most of us are, with a very small percentage of great professionals in a classical gaussian distribution.

But people that impressed their former colleagues have queues of jobs lining for them. And that's where most of your focus should go if you want to have a career.