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.