How do you contact other founders?

I had that same question a while back. Seems like there's a pretty solid community of founders here on Product Hunt, but what has also worked for me is going to in person events in my city. I started attending CEO dinners, and I've met a ton of amazing founders that way. For me, networking is so much easier in person. So, I'd suggest looking around and seeing what events are taking place in your area!

LinkedIn with a good in-mail message. Best route is always getting warm intro'd.