So there was a bug a patch or two ago where your teammates will no longer follow you if they don't have a weapon equipped. I could easily fix that right now, but I'm in the middle of the desert with shitty computers that all consider my compiler an unknown threat. I mean ALL new computers consider compilers an unkown alien viral threat.
I'll be back home before New Years to fix this crap, but until then, make sure your teammates have a weapon equipped if you want them to follow. They will auto-teleport anyway so it's not a big deal gameplay-wise.