How to promote questions/get answers?

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Updating the question puts it on top of the question list, but that's only helpful if the right person sees it before it gets bumped down and off the front page again.

I just noticed a feature over on the Gazebo answers site that might be useful to add to this site.
http://answers.gazebosim.org/questions/

At the bottom of every unanswered question is a bold prompt asking the viewer if they know someone who might know the answer and it has a mailto: link that you can click on which will seed your email client with the link. That might help promotion of unanswered questions.

In my experience there are two reasons for questions not being answered.

1. The question is not done very well, e.g. missing basic information, formatting, structure, answer is in docs/tutorials/google, etc. The guidelines help and in this case an update is a good idea. Also when new information was discovered.

2. No one that has seen the question knows an answer. To trigger relevant people choose a valid title and use correct tags. Ideally reuse tags that are already in use as some people might selectively only look at tags they care about.