aren't there a dozen other platforms for buying/selling/giving away stuff? Like, craigslist, letgo, and facebook marketplace?
Also, all of those companies believed enough in their idea to raise funding and pay developers. You want someone else to build your thing for free, which I don't think is too inspirational. Maybe if you had a pitch deck and some designs that could illustrate your points I might believe you, otherwise it's just dev begging.