Facebook is in acquisition mode again. The social network is acquiring the fast-growing mobile-messaging start-up called WhatsApp for $19 billion in cash and stock.

Although Facebook is the world's largest social network, it views the acquisition as a way to boost its numbers. WhatsApp has more than 450 million users and is adding about a million users per day, according to Facebook co-founder and CEO Mark Zuckerberg.

In a message posted on his Facebook account, Zuckerberg wrote, "WhatsApp will complement our existing chat and messaging services to provide new tools for our community. Since WhatsApp and [Facebook] Messenger serve such different and important users, we will continue investing in both."

Facebook bought the photo-sharing social network Instagram for about $1 billion in 2012.

Source: Reuters