I can't think of a single company who has reached a critical-mass consumer audience and not been able to monetize. Sure, winds change, MySpaces rise and fall, but it wasn't a monetization failure.
Anecdotally, just a month ago I was walking and because i live in San Francisco I happened across a corner (Howard and New Montgomery) where there were ~20 girls about 13 years old being polled about their tastes, and the questions I heard waiting for my light was "Do you guys like smartphones?" ("yes", duh), "Is your phone more important than your TV?" ("yes", duh), and "What is your favorite app?" and the answer was unanimously Snapchat.
Snapchat is the teenagers answer to the question many millennials have fretted about -- "how will ppl born today deal with having all 18 years of their development online". The answer is: they don't put it online. It's peer-to-peer and temporary by social contract, even if the technology is imperfect.
So far, snapchat has played a savvy game. As an engineer, if they were based in SF, I'd consider working for them. They have tapped into something. Because my 28 year old wife has also been hooked on Snapchat for what seems like a lifetime now. Her most frequent contacts? Both of her 60+ year old parents, numerous cousins and aunts, etc. Her dad uses it to send stupid pictures that you might not expect from a 65 year old white haired CEO-type whose work is about as far away from tech as you can get.