User blog comment:Blueyhale/How do World Eaters get around without psykers?/@comment-28917471-20150506104611

I think that they just make a lot of sacrifice rituals in honor of Khorne and let the Khornate daemons take them to warzones and other planets. There are also people that are called warp guides, like in the previous suggestion, they tend to "feed" warp entities, and in return, those creatures guide the vessel in the warp.

Again, the daemons can also send some messages and visions to their servants. I don't think that the world eaters are interested in keeping in touch with various traitor legions or other chaos warbands. But if Khorne needs them, then the war god will know how to reach his servants.