Recruiting more partners is like finding a good place to catch fish - go fish where the fish are, and recruit partners where they are.
One of the simplest ways to meet new partners and recruit new partners is to go where they are in person and online. Personally, I think having a good brand as a company and partner leader on social media is key to help to attract the right partners, and you should physically go in person to events where you can meet with partners and potential partners in person. In my world of enterprise sofware as a service, this is events like Dreamforce or Gartner.
One other key thing to point out is that many times, the best partners are already listed in other ecosystems and just need to go find them. One example I love is Zapier,
https://zapier.com/experts , powered by PartnerPage. This makes it so easy for you to find new partners in adjacent ecosystems.