My community has grown in fits and starts over the years. There are long lulls of a stable user base, then we get an influx of users over the course of 3-5 days. Some of those users end up sticking around and the stable user base grows a bit and enters another lull. The process repeats several weeks or months later.
The problem is, I have no idea where these influxes of users are coming from. I'd love to reach out to the areas of the internet they come from, but I don't know where to reach.
We've tried talking to the various waves of users, but no one really remembers how they ended up here in the first place. Once and a while someone can point to a Facebook post or a Twitter message where we are mentioned, but so far none of those have been posted around new waves.
How can I track inbound traffic and user retention so that we can plan our out reaches?