I tried an experiment earlier that I'd like to share. Searching google, using a modifier to search pages posted in the previous hour, for "D&D", I got a total of 46 hits. Two of those were chance uses of "D&D" that had nothing to do with the game. The remainder was content mostly produced by individual creators. Three were associated with the WOTC.
Taking those that were privately created, 41 total, we might extrapolate an average of 984 pages per day. Some of those posts may be repeats, but then none of them were posts in a foreign language, so we might suppose that non-English posts about Dungeons and Dragons could easily take up the slack. Let's just assume an average of 1,000 postings per day, most likely by single individuals, giving us a reasonable figure for how many people playing the game decided to post content about it.
We used to say in journalism that for any letter written to the paper expressing a particular opinion, there were about 100 people out there who felt just as strongly who did not bother to write. We might then argue that on any given day, there are up to 100,000 people thinking deeply enough about D&D to have a strong opinion, though most do not write about it.
These would be the Alphas in the game. People working, striving, thinking and writing down ideas about Dungeons & Dragons. It doesn't include people thinking about other RPGs, just D&D. For any Alpha, it is reasonable to suppose there are between 2 and 10 Betas ... it is really up to the reader to decide what a believable figure might be. From my experience, any time I have been around participants of D&D, I'd say about 1 in 5 is invested enough in the game to have a strong opinion about it. The other four are ready to play, but that one participant is really into the game, is really ready to talk about it.
This is the first time I feel I can point to a rational measure of how many people out there are playing today. Half a million. People can argue my statistical framework is weak and all conjecture ... and it is. I don't deny it. But it cannot be denied that 41 people sat down and wrote something on the internet about D&D in just the past hour. And no one can think those were the only 41 people on earth this last hour who were invested in the game.
Incidentally, I used the same method and looked up kayaking. 50 results for the past hour. Every result was a business trying to sell a location or a piece of equipment for people wanting to kayak. There wasn't a single post about a kayaker writing about his or her experience.
Think about that. The only reason we're invisible is because we don't exist as a market.
We do, however, exist as a tribe.