NEW YORK — Facebook is buying mobile messaging service WhatsApp for up to $19 billion in cash and stock, by far the company's largest acquisition.
The world's biggest social networking company said Wednesday that it is paying $12 billion in Facebook stock and $4 billion in cash for WhatsApp. In addition, the app's founders and employees will be granted $3 billion in restricted stock that will vest over four years after the deal closes.
The deal translates to roughly 9 percent of Facebook's market value and is bigger than any acquisition made by Google, Apple or Microsoft.
Google's biggest deal, Motorola Mobility, stood at $12.5 billion, while Microsoft's largest was Skype at $8.5 billion. Apple, meanwhile, hasn't done a deal above $1 billion.
Facebook says it is keeping WhatsApp as a separate service, just as it did with Instagram, which it bought for about $715.3 million.
WhatsApp has more than 450 million monthly active users. In comparison, Twitter had 241 million users at the end of 2013.
Facebook CEO Mark Zuckerberg says WhatsApp is on path to reach a billion users.
"The services that reach that milestone are all incredibly valuable," Zuckerberg said.
Shares of Menlo Park, Calif.-based Facebook slid $1.12 to $66.94 in extended trading after the deal was announced.
AP Technology Writer Michael Liedtke contributed to this story from San Francisco.