The most effective way is to get people interested in Go to boost their reputation on whatever Stack Exchange site best matches their interests. On a busy site, you can get 200 reputation in two hours or so, just having fun answering questions.
So the right question is now "how can I get more involved committers" but "how can I get committers more involved".
If you committed, but don't have rep over 200 on any SE site, pick the site that best aligns with your interests and spend two hours or so using the site. Answer questions, vote on things, be helpful. It'll be fun. And before you know it, 200 reputation will be yours. Don't be discouraged if you don't see your reputation going up, it will take some time for people to upvote your answers, so your reputation will keep growing even when you take a break.
This will also help with the commitment score. So don't think it doesn't matter once you have enough committers with >200 rep.