Three men charged with seeking to buy sex from what they thought were prostitutes in Boston have paid  $1,000 fines – forking over some of the highest penalties to date for such crimes in the state, the Suffolk County District Attorney’s office announced this week.

The news comes several months after the New England Center for Investigative Reporting found that despite a tough 2012 law meant to curb the demand for sex trafficking in part through stiffer fines, not one of the 11 District Attorney’s offices in the state could cite a case where so-called “Johns” were charged even a minimum mandatory $1,000 fine for attempting to buy sex.

Jake Wark, spokesman for District Attorney Daniel F. Conley, said these three cases represent increased efforts to hold men accountable for their participation in the US sex trade. Last fall, Wark told NECIR that the District Attorney’s office would press to increase penalties for sex buyers. The District Attorney’s Office also is pushing the legislature to create a statewide so-called “john school” for first-time offenders – to help dissuade men from participating in the often violent sex trade industry, which can victimize both girls and women.

“The average age of entry into the sex trade is in the young teens,’’ Conley said in a prepared statement. The three men -- Christopher M. Mudry of Lexington, Steven Pelletier of the South End, and Jeffrey Shyu of Brighton – “resolved their cases” by paying the fine and watching a video about the risks of prostitution, a news release said.

Each of the three, none of whom had a criminal record, was placed on pretrial probation and will have their cases reviewed in a year, Wark said. The three joined a total of 18 men who were charged in two related online prostitution stings orchestrated by the Boston Police Department last month. Some of the men were charged with seeking to pay for sex with money and others by buying sex with drugs, including Percocet and cocaine.

The other 15 cases are still ongoing, a news release said. The District Attorney’s office released names and pictures of the arrested men – an act seen by many as an important deterrent for others considering heading to the street or the Internet to buy sex.

Michael Shively, a Cambridge-based researcher who studies sex buyers, said that fear of higher fines as well as what is known as “public shaming” – including the release of photos -- likely will be a strong deterrent. “It's good to see substantial arrests and it is good to see substantial fines,” he said.