As much as $10 million.
That is the valuation investors have assigned to the new smartphone app whose sole purpose is to let people send text messages saying “Yo.” The app, appropriately named Yo, became an instant sensation in the technology world when news broke last month that it had raised $1 million from investors.
On Friday, Yo formally announced that seed investment round, which grew to $1.5 million. The investors included the technology incubator Betaworks and Pete Cashmore, the founder of the news website Mashable.
The company did not disclose its valuation in the round. But a person briefed on the matter, who was not authorized to discuss it publicly, said the investment came in the form of convertible notes, implying a valuation of $6 million to $10 million.
The challenge now for Yo will be to prove it is worth that much. The app, which debuted in April, has been downloaded two million times, according to Or Arbel, the chief executive. Betaworks said that more than 2,000 independent developers were working on projects built on top of the interface.
One such project emerged in Israel, where developers created a service using the Yo app to alert people to rocket strikes.
Mr. Arbel insists the possibilities are numerous.
“It’s not going to stay the same. It has a lot of potential,” he said of the app. The investors, he said, “invested in the potential.”
Betaworks, Mr. Arbel said, had been in discussions with Yo since May, “before anyone heard of the Yo app.”
The investors at Betaworks were early converts. Since the meeting in May, the app has “become part of our communications flow at Betaworks and in my life,” John Borthwick, the Betaworks chief executive, said in a blog post on Friday.
“We Yo with co-workers alerting them that a meeting is starting, I Yo with my wife as a hi during a busy day. I Yo with friends, without any more expectation or need than a Yo back,” Mr. Borthwick wrote.
“We are fascinated by these uses of simple yes/no on/off communications tools,” he added. “There is no payload in Yo — no pictures, no text, just a deceptively simple on/off state that over time has the potential to become a platform.”