Same as what xxr said below. Meetups.com usually will list informal or formal get togethers. Could also email your local startup association/incubator and ask. They may know of people hanging around or coming out of a startup and are looking for a new project. Also check out reddit subs /r/startups and /r/entrepreneurs I see a lot of "marketing experts" on there, however I would take anyone on the internet claiming to be an expert or a "growth hacker" with a grain of salt.