Snapchat is one of the 'classic' millennial apps

Snapchat is the latest unicorn to stumble, as investor Fidelity reportedly cut the value of its stake by 25 percent between June and September. The company was valued at $15 billion in its last round, according to reports, which is about 150x expected revenue this year.

But it's worth remembering why Snapchat had such a sky-high valuation in the first place. According to Comscore data charted here by Statista, Snapchat has captured the millennial mindset - more than three-quarters (76%) of the app's users in the United States are between the ages of 18 and 34. That's an extremely valuable target audience for advertisers.

It also helps that Snapchat is the fastest-growing social network among US teens, too.