I've heard of people having some success with https://www.cofounderslab.com/ but overall you just have to get serious about networking at technical Meetups, etc. It really depends on your geographic location. In some cities this is easier than in others. I have cofounders in different states, so if you organize your remote communications well that is an option. I'd be happy to discuss this topic with you.

I would suggest you go to Hackathons, Startup Weekends (or similar), check out Meetup.com for mixers where people that have the skills you are looking for are hanging out, and generally get out and network.

If video games are you thing, then join a new online guild for a game you don't normally play to get outside your comfort zone and meet new people.

The best way to convince someone to join your project is to find someone you genuinely want to hang out with for the next few years because you will be spending a lot of time with this person (or persons), and you can only do that with good old-fashioned face time.

angel.co many startups there and also founders