The IT specialist pleaded guilty in a district court yesterday and would be sentenced on March 10 this year, The Straits Times reported.
The accused, who cannot be named for legal reasons, faces 10 years in jail and a fine.
The minor, who is a Chinese national and was then 15-years-old, had responded to an online advertisement seeking an "extra man" in sexual trysts put out by the accused in October 2012, claiming that he was 18.
The accused then asked the two to engage in sexual activities and at one time joined in.
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The minor filed a police report on January 9 last year after his photographs were seen by his friend on the internet.
Pressing for a deterrent sentence in court yesterday, Deputy Public Prosecutor Kavita Uthrapathy said the accused had recruited the 15-year old to be part of his twisted sexual fantasies.
"The accused did nothing to ascertain the boy's age, and instead took advantage of his obvious naivety by making him do lewd acts.
Arguing that his client had never expected someone under 18 to respond to his advertisement, Defense Counsel Vinit Chhabra called it an "extremely heavy price to pay for a hobby gone wrong."
The lawyer claimed his client was in no way responsible for the photos making their way to the internet.
"My client didn't venture into the kids' world to purposely and intentionally take advantage of a young person," Chhabra told District Judge Victor Yeo.