Criterion Capital Partners bought the social network from AOL in 2010 but after struggling to turn it around filed for Bebo to go into Chapter 11 bankruptcy this week. Birch and his wife and co-founder, Xochi, bought the site back in an auction.
Birch and Xochi had been strategic advisors to Criterion Capital Partners.
Birch announced his acquisition of the company in a Tweet and said: "Can we actually reinvent it? Who knows, but it will be fun trying."
Bebo will now be revamped by Birch's idea lab, The Monkey Inferno, using its team of 21 engineers, designers and product people.
The Monkey Inferno is keeping quite about their exact plans for the site, but in a media release Shaan Puri, the company's chief executive, said: "We're excited about the ambitious challenge of bring Bebo back, and couldn't be happier to announce that the produce will be back in the hands of founders."
He said: "We know the odds are stacked against us, but we love challenges and the Bebo users deserve better than what they have received the past few years."
When Bebo was sold to AOL the site had 40 million users and was known for its high engagement as users spent over 40 minutes a day on the site. However it struggled with emerging competition from the likes of Facebook, Tumblr and YouTube.