CAIRO — After the security forces raided the home of Islam Khalil, a 26-year-old salesman, last summer, he seemed to vanish without a trace.

Mr. Khalil, who lives about 50 miles north of Cairo in El Santa, Egypt, had not been formally arrested, so his family could not determine where he was being held, or by whom. His relatives, who said he did not have access to a lawyer, worried that he was dead.

When Mr. Khalil finally emerged, four months later, at a police station in the port city of Alexandria, Egypt, he looked dirty and emaciated, according to his brother Nour, and reported that interrogators had suspended him from his arms and his legs, and administered electric shocks to his genitals.

“He didn’t look like the Islam I know,” Nour Khalil recalled in a recent interview.

Mr. Khalil is one of hundreds of Egyptians who have recently been subjected to what human rights groups call “enforced disappearance,” a harsh tactic that has become increasingly prevalent in Egypt as the government of President Abdel Fattah el-Sisi widens its crackdown on opponents, real or imagined.