Facebook, the social networking platform with more than 150 million registered users, celebrates its 5th birthday on Wednesday.

Facebook, regarded as one of the world's most popular websites, celebrates its birthday by sending mystery gifts to some of its registered users. The site's founder, Mark Zuckerberg, also posted a celebratory message on his Facebook blog. Facebook also has a photo album that shows how the site has changed over the last five years.

Facebook has grown a lot and expanded rapidly from social networking for Harvard and U.S. colleges to include high school, work networks, live and mobile chat and a platform for user-generated applications.

Its growth has made the site what researchers have called a social networking phenomenon, forever changing how friends, families and co-workers communicate with each other online.

The 24-year-old founder promised to continue to work hard on the development of the site.

Building and moving quickly for five years hasn't been easy, and we aren't finished, Zuckerberg noted in a blog post as we celebrate Facebook's 5th birthday, we continue to work hard to evolve Facebook and make it as simple as possible to communicate with and understand the people and entities that matter to you.