It only took seven days and a billionaire's gift to revive celebrities who had unplugged from social networks – including Twitter and Facebook – to raise money for an AIDS charity.

Lady Gaga, Kim Kardashian, Alicia Keys and Justin Timberlake were among the celebrities who gave up their online lives starting on December 1, World AIDS Day, until $1 million had been raised for Keep a Child Alive (KCA), the Brooklyn-based non-profit group co-founded by Keys that provides vital antiretroviral (ARV) therapy for children and their families with HIV/AIDS in Africa and the rest of the developing world.

Pharmaceutical entrepreneur Stewart Rahr's $500,000 gift on Monday brought the stars back on-line.

“I'm back from the dead! Thank you all so much for your donations and contributions! I have missed u all so much!!!” Kardashian tweeted her followers.

In a statement released Monday, KCA said 3,600 people had donated.

“Although we never expected to raise $1 million overnight, we are completely blown away that we were able to achieve our goal in less than a week,” the charity said.