SAN FRANCISCO (March 21, 2013)--YouTube says more than 1 billion people now visit its online video site each month to watch everything from zany clips of cute kittens to sobering scenes of social unrest around the world.

The milestone marks another step in YouTube's evolution from a quirky startup launched in 2005 to one of the most influential forces in today's media landscape.

YouTube crossed the 1 billion threshold five months after Facebook Inc. said its online social network reached that figure for the first time.

The vast audience has given YouTube's owner, Google Inc., another lucrative channel for selling online ads beyond its dominant Internet search engine.

Google bought YouTube for $1.76 billion in 2006 when the video site had an estimated 50 million users worldwide.