Yea I wondered about Grinder. I imagine a lot of people had the app and had it open in that area on that night. Late night, bars are about to close and you haven't found anybody yet (or in Joey's case you said "byeee" to a date who was a dud), so you look to see who is around, send out a few messages to the ones who look OK, and go from there. I feel like this is something police know about though and would have checked by now? It has been a few weeks. Grinder would cooperate with police in this situation. They should have had a lead by now.
Of course if somebody CAN see his location and was there nearby, they easily just could have scanned the bar and found him without messaging him. It is highly possible he was slipped something and he went willingly with that person. It would also explain why he didn't go back to his table and let them know where he was going. Geez it is scary. Whatever happend, if there is a person out there responsible, that person is just sitting there waiting for dust to settle and it could happen again.
And if I haven't said it before, I am so freaked out by the dating apps and social media. I have young kids. Is it OK for me to hope that this stuff just falls off of the face of the planet in the next 10 years?!