Some publishers, game makers and e-commerce companies are using the apps as a new distribution and moneymaking platform. Developers have been expanding the uses of the apps, making new functions possible. And investors, seeing huge potential, have driven the apps to ever-higher valuations.

“The most popular apps that sustain themselves day after day, month after month, at the top of the leader board, are messengers,” said Fred Wilson, managing partner at Union Square Ventures, a messaging app popular with young users. “That’s a reflection of what people do on their phones.”

He added, “Once they become full-blown ‘portals’ for mobile content and mobile commerce, we will really see how massive this opportunity is.”

The initial appeal of the apps is simple. They are faster to use than email, and they generally allow you to send text, links, video and photos to friends more cheaply than traditional texting services offered by wireless carriers like Verizon or AT&T.

The uses are multiplying, though. For example, people can discover other new smartphone apps and share them with their friends. On Snapchat, users can send money to one another inside the app. And Line, a messaging app popular in Japan, lets people pay for things at brick-and-mortar retail stores using Line Pay, the company’s payments service.
“Media and communication are converging,” said Jonah Peretti. “Some of what we’re all creating now will be a huge part of these messaging apps over the next one or two years.”

Now, 40 % of mobile subscribers in the United States use an instant messaging app on their phones at least once a month, according to data from comScore, a research firm. Globally, the use of mobile messaging apps grew 103 % during 2014, according to Flurry, a mobile analytics firm.

Some of the most popular options are Viber, which says it has more than 200 million monthly visitors; Line, Japan’s most popular messaging app, with 170 million users; and WhatsApp, the leading service, which has more than 700 million regular visitors.

For now, though, not all of the apps are generating big revenue. WhatsApp, which is owned by Facebook, reported just $10.2 million in sales in 2013. The revenue came from the small fraction of users who paid $1 to use the app.

Still, the valuations of many messaging start-ups continue to rise. In February, Rakuten, the big Japanese online retailer, bought Viber for $900 million. The next month, the Chinese e-commerce behemoth the Alibaba Group led a $280 million investment in Tango, valuing the nearly six-year-old start-up at about $1 billion. Facebook paid $21.8 billion for WhatsApp in February.
Many entrepreneurs see WeChat, the hugely popular Chinese service run by the Internet giant Tencent, as the ideal model for building a business in messaging. Released four years ago, the app now claims nearly 500 million monthly active users — who not only send image-laden messages, but play games and book car rides and plane tickets.

The rapid growth in messaging apps, some say, has been a response to the more public nature of popular apps like Twitter and Facebook, where status updates and posts are visible to the many rather than the few.

“It’s a much more intimate experience,” said Marissa Campise, a partner at SoftBank Capital, the venture arm of Japanese telecom giant SoftBank. “Messaging apps are smaller and less visible than the public networks and far more engaged and trusted. It often feels like a more controlled, real-time replacement for email,” she said.

Messaging users tend on average to pick up their phones several times an hour, Talmon Marco. That makes messaging apps an ideal place to introduce other offerings like games, virtual stickers or even physical goods.

Asia has been a particularly fertile breeding ground for expanding the uses of the apps. In 2013, for example, WeChat joined Xiaomi, the Chinese smartphone giant, to offer a limited quantity of the company’s newest phone for purchase on the chat app. Users could reserve and then buy the new smartphone entirely inside the WeChat app using Tenpay, the payments service owned by Tencent. Xiaomi said it sold 150,000 phones in less than 10 minutes.

The WeChat app is also one of the biggest hubs for Chinese consumers to find new mobile games. Last quarter, Tencent’s mobile games revenue alone was 2.6 billion renminbi, or about $420 million.

“They’re aggregating people’s attention and linking it to other forms of commerce,” said Mitch Lasky.Ted Livingston has argued that younger users are coming of age in a world where their portal to the Internet has been the smartphone, and they are more willing to try new forms of commerce and discovery.

“We view this as being a race to be the WeChat of the West,” Mr. Livingston, whose app is predominantly popular with young North American audiences, said in November. “For us, it’s a once-in-humanity great opportunity.”