According to sources familiar with the matter, Snapchat has filed for an initial public offering (IPO) that could value the company at $25 billion, making it the largest IPO since Chinese e-commerce giant Alibaba Group went public two years ago. Reuters reports: Snapchat filed with the Securities and Exchange Commission under the U.S. Jumpstart Our Business Startups Act. Companies with less than $1 billion in revenue can secretly file for an IPO, allowing them to quietly test investor appetite while keeping financials confidential. A Snapchat IPO is seen by many investors as a bellwether for many of the largest so-called "unicorns," private, venture-backed companies that are valued at more than $1 billion. Nicknamed "decacorns," these companies are valued in the tens of billions of dollars and include Snapchat, car-sharing company Uber Technologies Inc and home-sharing company Airbnb. No decacorn has yet tested the public market, and it is unproven whether they can beat or even replicate such astronomic valuations with more scrutinizing public investors. Snapchat started in 2012 as a free mobile app that allows users to send photos that vanish within seconds. It has more than 100 million active users, about 60 percent of whom are aged 13 to 24, making it an attractive way for advertisers to reach millennials.