The vast majority of them are in Asia. The self-help industry has cultivated a thriving trade in selling Eastern spirituality to spiritual-but-not-religious Westerners, but the pop-culture Buddhism they’re proffering doesn’t really sell Buddhist mysticism very well. Instead it mostly just feeds into the monstrously-massive “New Age” market segment. Little tidbits of wisdom here and there. Few dharma books of any substance.
There are Western-based mystic pathways that you can find, but that’s the nichiest of the niche niches. (Nietzsche?)
On the whole, I would estimate the number of serious aspirants in Asia to number in the hundreds of thousands, amongst a population of perhaps 2–3 billion. In the entire rest of the world, I would estimate in the tens of thousands collectively.
If I were to estimate the number of actual enlightened people, it would be in the thousands in Asia, and in the low hundreds in the rest of the world. I would guess that while fewer people are interested in enlightenment in the West, more that are interested actually achieve it.
Note that I don’t think Asians are somehow worse at following the path than Westerners. Mysticism is a tough path to follow, and in the West you have to actually seek out the path before you can walk it, whereas in Asia there’s a guru on every street corner. So the few Westerners that find it are more motivated. Also this doesn’t count enlightened people that didn’t need mysticism in order to become enlightened, like myself. That number is impossible to estimate.
Anyway, that’s my rough, back-of-the-napkin estimate.