The first piece of advice for collaboration first-timers from many professionals in this space is that it can be fruitful to work with people you already know. You've already established trust and communication, which are incredibly important to making a collaboration work.
It can also be useful to start a large partnership with a smaller core group, which you can assemble with people you know.
If you're looking to branch out beyond your network, here's how you can find potential partners:
Start from the bottom up. Research individual reporters based on their beat. Who's doing solid, interesting reporting in this space and would be excited about new reporting opportunities? Energetic beat reporters make for some of the best partners, and they can serve as boosters for the collaboration inside their newsroom.
Identify the major players in a given city or state. Who's doing good work in print, radio, TV and digital? Are there nonprofit or hyperlocal newsrooms?
Make connections at industry conferences. It's a great place to meet face-to-face and find people working on similar issues or projects.
Once you’ve got a good list of potential partners together, there are a few ways to reach them.
If you have friends in common, it can be useful for them to put you in touch. It helps build trust.
Cold emailing. Set up calls or in-person meetings via email to tell potential participants about the project. Email is a good starting point because you can lay out a basic description of what you're trying to do ahead of time. It's helpful to start with the reporters who would work directly on the project, who then can get buy-in from the higher-ups.
After you announce the project, recruit participants at industry events. One way to do that is to do a panel or talk about the project as a starting point and pitch a group of people at once.
Post and circulate a sign-up form to allow participants to come to you.