If you listen carefully, you'll see what this is about in Liz Gannes' writeup:

“We want to become a billion-user company,” said Wattpad CEO Allen Lau. “There are five billion people who can read and write on this planet, so a billion users is totally achievable.”

Well, a billion is still well in the distance, but Wattpad is currently at 25 million monthly users, who write 150,000 stories per day. The growth and loyalty of its readers and writers have enticed venture capitalists to invest another $46 million into the company, which has now raised a total of $67 million.

Last time Wattpad raised money, about two years ago, it had eight million users. Since then, it’s also grown from 15 employees to 70, all based in Toronto.

The site is home to all sorts of stories, many of them told in installments, including lots of romance, fantasy, sci-fi and fan fiction.

One interesting note is that 85 percent of Wattpad usage is now coming from mobile devices. As expected, that’s mostly time spent reading, but Lau said a surprising number of authors write from their mobile devices as well.

The new funding came from OMERS Ventures, August Capital, Raine Ventures, Northleaf Venture Catalyst Fund, Union Square Ventures, Khosla Ventures, Jerry Yang, Golden Venture Partners and Boris Wertz.

Amazingly, August Capital partner David Hornik wrote a loosely fictionalized version of getting pitched by Wattpad — on Wattpad. It’s great fun for the digs at himself and his less-than-on-time VC partners.

As for a Wattpad business model, Lau is unconcerned. “Our main focus is on user growth,” he said. “All our numbers are growing, hockey-stick style.” Today Wattpad has some limited advertising; down the line there may be paid products and native advertising, Lau said.

85 percent of the usage on mobile means that mostly people read on Kindle, tablets, and smartphones.

Fanfic, romance, scifi, and fantasy are huge on Kindle.

The reason Wattpad is so successful specifically is One Direction Fan Fiction:

http://www.businessinsider.com/wattpad-app-for-android-and-iphone-2014-4

Investors have referred to the app as the "YouTube of Writing." In an interview with GigaOm's Matthew Ingram, one of Wattpad's primary investors Andrew Chung explained how this could be used as a tool for discovering new writers:

You’re able to upload a story chapter by chapter, folks are able to comment on that chapter, and they can provide encouragement to the writer and actually signal where they’d like want the story to go, which creates a type of engagement that’s impossible in an offline context. There’s a very strong parallel to the way that YouTube was able to do that for amateur or user-generated video content.

Seriously, Google for any of these terms:

Wattpad One Direction dirty

Wattpad One Direction fanfic

Wattpad One Direction imagines

Wattpad One Direction preferences

Wattpad One Direction bit me

Wattpad One Direction babysitting

Wattpad One Direction rated r

Wattpad Justin Bieber rated r

Wattpad Justin Bieber love story

Wattpad Justin Bieber dirty

Wattpad Justin Bieber imagines

Wattpad Justin Bieber fanfic

...Seriously!

For what it's worth, micro-installment writing (often people writing novel-length works on mobile devices and releasing them a page at a time) in Japan has launched the careers of many authors.  A good chunk were able to transform online popularity into printed book deals.

That's cool. Am I correct in thinking that 140 characters of writing in Japan is like a page of text so Twitter is actually useful for something like this?