The channel that will work best for you depends on the niche your site is in.
Since you state you would be recruiting these teachers, I'm presuming it's a paid position.
Here are some strategies:
- Post ads on craigslist
- Post a "remote ok" job on AngelList and other relevant sites where you audience is. i.e. AngelList would only work if you're recruiting software engineers, designers, or marketers.
- Figure out which meet-ups your audience attends, and try to recruit them in-person.
- Graduate students are usually willing to teach their newly learnt skills. You could pitch to them as an internship.