If we strip the sentence of all the modifying phrases, we are left with: "38 percent has used the services––more people than were using it." The dash is now joining two independent clauses, which the dash doesn't do. Also there is a comparative "more...than" without a reference "that." Would this sentence be acceptable: "I like apples bigger than in my cereal." Or, "More doctors than are prescribing Xanax this year."
I would rewrite the sentence: "As of 2014, 38 percent of the world's population has used the services of the Internet within the past year—a hundredfold increase from 1995."
Dashes seem to be wild cards in writing: everyone has their own set of justifications / rules / recipes / guidelines for using them. Dashes are like like spicy foods––some people like them, others don't. This writer thinks of them like pauses http://opinionator.blogs.nytimes.com/2012/10/22/mad-dash/?_r=0, this website uses dashes to set off appositives http://writingcenter.unc.edu/handouts/semi-colons-colons-and-dashes/ The trouble with thinking of dashes like pauses is that what follows the "pause" might be ungrammatical or unclear. A recent post about Wittgenstein's writing is a case in point Long dashes between sentences. I used the dash in my rewrite because I feel "a hundredfold increase" is further describing "38 percent."
On a side note, do we really need to say "human" population? Who else is using the internet, spiders?