Most friend groups have a dormant version of themselves: the people you were close to at university, the old team from a job two roles ago, the crew from a place you used to live. Everyone agrees you should see each other more. Almost nobody makes it happen, because reunions need one person to do the unglamorous organising, and that role tends to go unfilled.
Be the organiser, openly
Reunions do not happen by consensus. They happen because one person decides to make it happen and accepts the small awkwardness of herding people. You do not need permission or a perfect plan. You need to pick a rough date and put a stake in the ground. The group has been waiting years for someone to do exactly this, and they will be relieved it is finally happening, not annoyed that you took charge.
Solve the everyone is scattered problem
Old groups are usually spread out, across cities and across apps. Half of them you have not got current numbers for, some have left the platforms you used to share. This is the practical reason reunions stall: there is no single channel that still reaches everyone. The way around it is to invite by whatever you have for each person, an old email, a number, a link passed through a mutual friend, and let them RSVP without needing to join anything. You do not need everyone on the same app. You need everyone pointed at the same event page.
Pick a date far enough out
People with established lives need lead time. A reunion thrown together for next weekend will get apologies, not attendance. Aim several weeks out, ideally with a couple of date options so you land on the one the most people can do. The further the scattered group has to travel, literally or in terms of rearranging their lives, the more notice they need.
Keep the bar low
A reunion does not need to be a weekend away or an elaborate event. The fantasy version, a whole trip, a big production, is exactly what stops these from happening, because nobody has the energy to organise it. A long lunch, an afternoon in a park, drinks at a pub that will have you for four hours. The simplicity is the point. The reunion is the people in the room, not the itinerary.
Use it to restart the rhythm
The best outcome of a reunion is not the one night. It is that the group remembers it likes being together and agrees to do it again before everyone scatters back into their lives. Before you all leave, pin down the next one, even loosely. The first reunion is the hard one. Turning it into a recurring thing is how the group actually comes back to life.