Great idea, I'd do it somewhat like this if i had a large enough team:

features needed to be successful:
--STack overflow/HN/Reddit style Rep or magical internet points: These things are important, look how compelling they are for people to go out of their way to do things.... If you can tap into this so people go out of their way... to leave their house and socialize. even if its superficial for internet points, its helping adn putting them in the right direction.

--badges, via Audible App/Duolingo App, and other big sites that have probably spent big $$$$ coming to the conclusion that these things increase engagement. Have badges for 'hung out with same person in same meetup event 6 times in a row...(having social interactions with the same people over and over again builds better connections.) also: hung out with a newb (low reputation) and a (insert great noun here warlock/mage (gender neutral)/pilot etcc.) basically a veteran socializer in same group.(sub point... people can get different avatar badges i dunno anything to make it optionally fun/kooky not so serious, adds a great common talking point when players (social players) get together in a meetup.

--these things can also be refactored to mimic Riot games 'League of Legends' game, a free to play game, that is the #1 esports game in the world, with more viewers than NBA finals. They use 'riot points' as a way to make $ so players can customize / stylize/express uniqueness in game with skins on base models... anyways point being that there oculd be points like this which allow people to 'enhance a meetup' so anyone attending gets a bunch of rep, or gets a hat, or gets a badge etc etc... maybe it costs the person activating it 10$, but its totally worth it for them cause the nerdy players coming are psyched for the __Free__ magical internet points or magical virtual hat or whatever. Also you can tie it into businesses and volunteer organizations in your local town. Like, meetup at foodbank berlin, foodbank Newyork, southside to volunteer and get XXXX extra points, or increase your volunteer badge etc.. heck put in a talent-tree a la duolingo/diablo for volunteering advancment haha (this step would require late stage company growht with lots of emplyees / communtiy mgrs and operations to avoid corruption and loopholes in this system)

At the end of each meetup have an optional form players can fill out ascribing strange nouns or adjectives to other players (green rooted dandelion, extreme fluff shark, ported slime swamp) a la heroku/gfycat slug style. They wont ever know, the exact attributions they receive but every 6 months some strange algorithm takes the inputs and generates a strange pokemon style creature or item and gives it to them.

then fractal-idea-spiral off this and include them in meetup invites with other players who have been given randomly given similar creatures. so then the commonality in that unique meetup is the strange-ass reward they receive in this game.

also see Yelp, and how they have community events, could probably snipe some ideas from that to increase peoples local engagement in this. Or, plug into yelps api and have food based events where people meetup based on local deals restaurants are having. then have sub games inside the meetup like who can take the best photo of a drink shrine, where everyone stacks their drinks/cans of sodas in an intricate pattern, or who can make the best fries shrine or some weird art construction thing like that. they are all passed into a NN-imageclassifier you have running that tries to accurately match em to ancient temple shrines as well as pictures of fries etc...make up some function to give each picture a score. whatever the challenge is. This is crazy dumb, but thats the point its some kooky dumb thing they are doing together and its fun its social. also great press cause it will generate weird headlines.

There would be lots of features/game modes in this app, the food one above being an example. so like LeagueOfLegends, make some of them unlockable (2-5$), but have them on 'rotation' so they are always playable eventualyl throughout say, 2-3 months, also players can eventually unlock em wihtout paying, by using the points they accumulated.