The girl, identified by the pseudonym Xiaowen, was admitted to a hospital in Xinyi, Guangdong province, where an abortion was performed on Saturday. Police forensics officers are investigating.
According to online news portal Thepaper.cn, the girl was just over one month pregnant when her condition was discovered by her family, who immediately called in the police.
The girl had undergone a previous abortion in March. At that time, the family reported she had been raped by five or six men.
Police had investigated six people, based on Xiaowens description, but failed to match DNA evidence with any of the accused.
Local police said in an official notice on messaging service WeChat that due to restrictions, such as the victims limited ability to communicate, there were few leads and the case was being continuously investigated. The notice said the latest case had been reported by the family in October.
The police call for the culprit to turn himself in as well as for the public to provide any information on the case, it said.
The Xinyi government said on WeChat on Friday that it had provided psychological counselling to the girl and her family, arranged the abortion and received donations from charity groups to help her study in a special needs school after she recovered from the operation.
Xiaowens aunt, surnamed Qiu, told Thepaper.cn that the girl lived with her parents, who also have mental disabilities, and an older brother.
Members of the public questioned how the girl could have been raped and impregnated twice within eight months and whether she was being adequately supervised.
The China Disabled Persons Federation issued a notice on microblogging site Weibo on Sunday, calling for the case to be solved and the rights of children with disabilities to be protected.
We will work with local associations and government offices to provide counselling, legal services and education, to protect the rights of people with disabilities, it said.
Sun Xuemei, co-founder of girls welfare group the Beijing All in One Foundation, told the South China Morning Post that proper mechanisms needed to be set up to protect young girls from sexual harassment.
In this case, an effective guardianship mechanism should be set up, we should explore designated foster care or care by charity groups, she said. But there are difficulties, such as finding a willing and capable foster family.
Studies by various researchers have indicated that about 8-12 per cent of Chinas 270 million minors faced some form of sexual assault, including about 1 per cent who were sexually penetrated, according to Shang Xiaoyuan, from Beijing Normal Universitys Family and Child Research Centre, speaking in May this year.