Samuel, aged just 17, was filmed performing a haunting rendition of Dion's The Power of Love while sitting barefoot on a staircase of his building in the central African country's capital Libreville.
The video was picked up by a prominent Gabonese logger and viewed more than a million times in a week before Dion reposted it on her Facebook page on Tuesday evening, doubling the number of views overnight to nearly 2.3 million.
"Samuel, your talent is as big as your voice. I'm touched my songs have travelled all the way to you and hope we have the chance to meet one day," Dion wrote on Face book.
"May all your dreams come true. Keep singing like you do. When music comes from the heart, it knows no borders!"
Samuel, from a poor family in Libreville, has never taken singing lessons and said he has had to leave school because of a lack of money.
He said he was "overwhelmed and very surprised" by the message from his idol.
"I wasn't expecting that. I haven't got a phone or a Face book account -- it was my brother who told me Celine had shared my video," he said. "I just hope that one day I can meet her for real."
While Samuel has a way to go to match Dion, whose emotional ballads in French and English have made her one of the biggest-selling singers of all time, his new-found internet fame looks to be opening doors already.
He said he has been approached by producers from TV singing contests in France and Ivory Coast. But the youngster is finding stardom an unfamiliar experience.
"I'm not used to this (success). I feel good when I sing in the staircase, and now people recognise me in the street," he said.
