Businessman Tang Boon Thiew who set up an online vice ring and earned about $185,000 from the trade will be sentenced next Friday afternoon.

The 39-year-old, who faces 102 charges, pleaded guilty to 20 charges - five of living on the earnings of prostitution, four of procuring women for prostitution and 11 of abetting to obtain the commercial sexual services of a minor.

The court heard that he procured 19 social escorts aged 17 to 43 for prostitution at different points between 2009 and 2011.

Investigations showed that only 17 of them had provided sexual services to customers during bookings secured by Tang.

He fixed different rates for different escorts based on their ages and physical attributes.

Based on Tang's records, he had secured about 700 bookings for the 17 escorts between September 2010 and November 2011.

The total prostitution earnings amounted to about $371,450 and his share was estimated to be half.

So far, 16 of the 51 men who had commercial sex with the 17-year-old minor have been jailed between nine and 13 weeks.

They included green activist Howard Shaw, who was released from prison on Nov 30, after spending eight weeks behind bars for paid sex with the underage prostitute, and former school principal Lee Lip Hong, 37, who was given nine weeks' jail. He is the first person to plead guilty to his charges.

The prosecution is asking for a total sentence of at least five years plus a heavy fine saying Tang's criminality is unprecedented and his conduct, alarmingly aggravated. But defence counsel Shashi Nathan said a sentence of 30 months would suffice as his client did not know that commercial sex with a person under 18 was an offence.

He said the University of Hull graduate has had an illustrious career, holding senior management roles at various well-known multi-national corporations he worked in, including oil-giant Shell and online search engine Yahoo.