tech/media platform question

So, hypothetically (because I won't know until tomorrow), if I wanted to gather a bunch of people to do something like a flash mob, what would be the best way to organize and give instructions? My plan would be to put an ad in the paper and/or on kijiji to reach the most people, but I need a way to get more specific with them.

These would be people that I don't know, so I don't really want to give out my personal email address to 1000 strangers, but I need to give out instructions as to where and when, and I also might need to put up a short dance video so everyone an learn the moves.

I would also like it if there could be some back and forth, people could ask questions, and/or I could get a head count of how many people to expect.

blogspot? facebook (which I don't use, and I think you need to specifically invite people to a special group??)any other social media platform that doesn't have to be linked to my rl. I could just start it up for this ,and then abandon it.

Thanks in advance!