Yeah, don't bother in the old world, especially not near the center. You might get lucky, but you probably won't. So far I've found two copper mines somewhere along the west edge of the new world and my friend found two copper, two tin, and one iron. It seems someone's taken the iron before we could setup, though.
In the old world, I searched from a bit west of the center to the south edge and then back to the equator for around 24 hours with no luck. You might find an abandoned mine or something, but your best bet is to head for the new world. Your first step is to find out where you are/which edge you're closest to (after you can see rustroot, of course).