The number of minors given guidance by police for making suggestive online posts, mostly for enjo kosai, or compensated dating, in 2015 shot up 32.9 percent on-year to 666, National Police Agency data show.

Of the minors, 519, or 77.9 percent, were girls, the agency said Monday.

The number of high school students surged 49.7 percent to 479, and that of junior high school students soared 64.4 percent to 74. Those aged below 18 increased 21.4 percent to 533, with the youngest aged 12 years old.

Of the total, 71.6 percent offered to engage in enjo kosai, and 21.5 percent intended to sell their underwear.

An NPA official said some minors readily sell sex for money, but the consequences are they may be threatened with the publication of naked photographs or be victim to other crimes, including kidnapping.

In October 2013, police across Japan started undercover probes in which they contacted minors online after finding their suggestive online posts. They then made appointments to meet face-to-face and offer them guidance.

In 2015, the number of cases in which police failed to contact minors who had made suggestive online posts totaled 14,716, up 33.2 percent.

Some police officers were unable to meet with the person although they made appointments, while others lost touch with their targets after the minors apparently suspected they might be police, according to the NPA.

In these cases, the minors might have switched their target buyers in order to avoid attracting police attention, an NPA official said.

Meanwhile, police identified 141 cases in which offenders contacted minors in 2015, including 93 for child prostitution and 14 for child pornography.