I can say from my experience so far with Buffer, that it is easy for this to get very hard to keep up with. Seems like they had similar great intentions like us to be amazing at support as well as build a fantastic product. We had a period where our support response time lagged as we reached a certain scale. We've since hired a freelancer for a few hours a day to help us and that's really transformed things to the point where we're better at support than we've ever been, and at the same time we can focus on what each of us in the rest of the team is good at. Whilst the freelancer does a lot, we dip into support every so often and have things assigned to us, so we're always in contact and understand customer problems, which I think is very important.

We used UserVoice for a while and were responsive, then as we scaled we found it hard to keep up with, and ended up good at our email channel but bad at our UserVoice channel. Since then we've improved again and are generally good at all channels. With this experience in mind, I'd suggest reaching out through multiple channels if you want to get through to them. Try email and Twitter as well as the obvious channel.