When you see on Twitter that he will be somewhere for 10 minutes you need to first, find the NPC that he is talking about and figure out what map that is. Then, once you do that you need to click your Globe ( World Map ), and click Join Game, and choose that same instance you are in, but look for a really populated one. To make this easy, type in the Campaign Name where it tells you, and check off the Town Only box.

I got a pair of antennas today for 6 of my 9 characters doing this.

Also, if you are still looking for him, he is gone.