Start making friends in the US, now. Look for meetups, find Facebook groups, figure out which companies have a significant presence in the area where you'll be relocating. You're starting from nothing with your social network but you already have valuable skills. Get to work on the networking now and you'll set yourself up to easily find work once you land ... if not sooner.
One thing that I am definitely planning on doing is sending emails to companies of interest some months before the move and just introduce myself. You're absolutely right though: networking starts now, but it is hard when I can't be there in person and go to meetups, etc.
