The singer took his Las Vegas show to The Dorchester hotel in Britain's capital, and he asked fans to pay at least $80 (£50) per ticket to raise funds for the Hold Amy's Hand appeal, which aims to raise $160,000 (£100,000) to help entertainment journalist Amy Watts as she battles colon cancer.
Goss says in a statement, "I recently lost my mother to cancer, and it was a life changing moment for me, if I had known three months earlier I could have saved her life.
"We are all very busy but not busy enough not to show solidarity and help this wonderful young lady. Every journalist, every photographer, every friend in the media and every friend of mine and Amy's please can and show your support."
Other stars backing the campaign include soccer legend David Beckham, music mogul Simon Cowell, pop star Kylie Minogue, former Boyzone singer Ronan Keating and members of Take That.