Best place to find a Co-founder who's also an App Dev?

I'm a Solopreneur and the only thing I outsource is actual coding of my mobile app after I have designed it.

I've noticed this is a weakness of my startup - where's the best place or best way to find a Co-founder that can help with App Dev to bring it in-house, in exchange for some of my startup?

Any tips on how to approach this situation?

P.s. this is my first time looking into this, so please don't crucify me!

Thank you