NEW YORK (AP) — Facebook is placing a $19 billion bet on reaching its next billion mobile users with the acquisition of WhatsApp, a popular messaging service that lets people send texts, photos and videos on their smartphones.

The $19 billion deal is by far Facebook’s largest and bigger than any that Google, Microsoft or Apple have ever done. But it is likely to raise worries that Facebook and other technology companies are starting to become overzealous in their pursuit of promising new products and services, said Anthony Michael Sabino, a St. John’s University business professor.