Why? Why do you do this? You are asking an unanswerable question. You want stupid answers? Okay, ten. Ten people are mining altcoins. Ten people and 1000 sock puppets for each of them, spamming and pumping and dumping. You might as well ask, "how many people are eating peanut butter and jelly sandwiches right now?"
The hashrate for a particular coin can be determined if you look at it's current difficulty and what the hashrate equivalent is, and from there at least you can guess how much mining hardware of a particular type might be employed.
Can you also tell us what is the best coin to mine and/or which one is going to the moon?
I honestly don't know what goes on in the heads of the people who ask these questions.