The first shock came when Mordechai Jungreis learned that his mentally disabled teenage son was being molested in a Jewish ritual bathhouse in Brooklyn. The second came after Mr. Jungreis complained, and the man accused of the abuse was arrested.

Old friends started walking stonily past him and his family on the streets of Williamsburg. Their landlord kicked them out of their apartment. Anonymous messages filled their answering machine, cursing Mr. Jungreis for turning in a fellow Jew. And, he said, the mother of a child in a wheelchair confronted Mr. Jungreis’s mother-in-law, saying the same man had molested her son, and she “did not report this crime, so why did your son-in-law have to?”

By cooperating with the police, and speaking out about his son’s abuse, Mr. Jungreis, 38, found himself at the painful forefront of an issue roiling his insular Hasidic community. There have been glimmers of change as a small number of ultra-Orthodox Jews, taking on longstanding religious and cultural norms, have begun to report child sexual abuse accusations against members of their own communities. But those who come forward often encounter intense intimidation from their neighbors and from rabbinical authorities, aimed at pressuring them to drop their cases.

Abuse victims and their families have been expelled from religious schools and synagogues, shunned by fellow ultra-Orthodox Jews and targeted for harassment intended to destroy their businesses. Some victims’ families have been offered money, ostensibly to help pay for therapy for the victims, but also to stop pursuing charges, victims and victims’ advocates said.