A man who friended more than 160 adolescent boys on instant messenger applications and persuaded at least three to have sex with him is still waiting for a court verdict that could send him to prison for up to five years.

Li Jun, an former official at the Civil Affairs Bureau in Guangzhou, Guangdong province, was accused by prosecutors of sending sex-grooming messages with a smartphone app to boys aged under 13.

He has become one of a string of suspects using phone-embedded messaging services to locate potential victims.

QQ Drift Bottle, an application used by Li, allows users to randomly throw a digital bottle with encoded messages to a stranger's phone.

QQ, the traditional online chat service developed by Tencent, claims to have more than 700 million active users, and its mobile messaging service Weixin can automatically import a user's existing QQ friend's list.

Public security officers from cities such as Guangzhou, Beijing and Hangzhou, where there is a large number of smartphones, have warned residents against such crimes.

Police from Hangzhou, Zhejiang province, said they have observed an increase in reported thefts and sexual assaults coinciding with the popularity of the high-tech gadgets.

"Weixin and similar services have facilitated robberies and sex-related assaults, including rape, since it is easier for perpetrators to find potential targets," the police said in a statement.

The Hangzhou police said they have seen some 20 Weixin-related theft and fraud cases since last December. Their counterparts in Beijing, where specific data are currently unavailable, confirmed seeing a similar increase.

An ifeng.com survey of 35,000 Web users was split almost 50-50 on whether app developers should accept partial responsibility for suspects finding victims. About 45 percent of those polled argued "gun makers should not be charged for crimes committed with their guns".

A sophomore named Wu at Guangdong University of Foreign Studies who said she has received anonymous sexually harassing messages on Weixin also suggested the developer add functions such as being able to block senders.

A spokesman from mobile messaging services Momo said the application is by no means designed to facilitate fraud and theft and that the company has been trying to tip users to potential risks by sending messages.

Dai Peng, a criminal investigation expert at Chinese People's Public Security University, said Weixin-related crimes are "old wine in new bottles", meaning that criminals are playing old tricks with the advantage of high technologies.

The essence of the crimes are not different from ordinary robberies and thefts, he said, just like other kinds of Internet-based crimes.

Dai said he believes application development companies should notify users to potential dangers they may face when using such services.

Contact the writer at zhaoyinan@chinadaily.com.cn