Looking for some insight into what processes, tools, features and functionality have been used successfully to optimize consumer communities like Reddit, particularly anything that's been used in mobile. Also trying to understand if companies do this in-house vs. empowering users (ala Reddit). What do popular social apps like Snapchat, Instagram, Vine, etc. to manage this?
Given the time it takes to moderate communities well, finding volunteers to do that for free is not likely. It is better to hire a community manager who already has experience who is willing to keep growing as communities change.
Reddit is a perfect example of a community that businesses would probably want to avoid. Why is explained in http://www.dirjournal.com/articles/reddit-guide-how-to-use-reddit/
Each community is different and requires different skills, tools, and strategies. Here are some you may find beneficial:
These posts explain the currently available tools for managing Instagram communities http://www.socialmediaexaminer.com/instagram-community/
Tips for using Snapchat
Strategies for Vine
There is a Google Plus Community Manager group where you can find discussions and strategies: https://plus.google.com/communities/101510889779807726729
You can find many more tips online such as Mashable's 12 Top Community Managers Share Their Tips for Better Engagement http://mashable.com/2012/03/15/community-manager-engagement-tips/
I hope these cover what you really wanted to know. We would need more specifics (platform, business, goals) to answer more clearly.