Having set up many a pin/DIS meet, I can help with this. Pick a date and stick with it since no matter what date you choose, there will be people who can't make it. Find a convenient place -we like mall food courts (ask for permission at the mall office). Then post the info. At first I brought in mylar Mickey & Minnie balloons to identify the meet but a local mall has banned them (not sure why). Now I will tell new people to look for the group wearing a lot of Disney.
Good Luck and if you have any other questions, feel free to email me.
Cyn