I've always wondered. Alexa has become unusable, and Trends was the only free thing I could find. One datapoint that it works: When I used Google Trends to claim "Reddit seems to have doubled since 2013," no one contradicted that: https://news.ycombinator.com/item?id=8567833

It seems like all tools are indicating that Reddit is growing like a weed, though. Actually, Reddit is in a pretty unique position. Subreddits mean that pretty much every person on the planet is going to find something interesting, so everyone from 13 year olds to grandmas are participating.

I wonder how long Reddit will continue to grow before people start comparing it to Facebook.