William Slemaker tries to comfort his wife, Maria Antonieta, as she recalls the last time she saw their daughter—a Friday last summer when the 28-year-old single mom stopped by the Laredo, Texas, cafeteria where Maria Antonieta worked. Recalling how the beautiful, dark-haired Yvette Martinez turned everyone's head when she walked in, then gave her mom a warm hug, Maria Antonieta begins to sob. When she can't go on, William, a train conductor, offers this plea: "We need her back," he says. "We just want her home with us."

The couple have endured this painful limbo since mid-September, when Yvette and a friend went to a concert in the Mexican city of Nuevo Laredo—just across the Rio Grande—and then disappeared without a trace. Though Slemaker, 43, now spends much of his free time in a desperate search—posting Yvette's photo and talking to anyone who will listen—he is only one of many. Since Aug. 15 the FBI in Laredo has investigated 30 cases of U.S. citizens going missing in Nuevo Laredo; two turned up dead and 13—including Yvette and friend Brenda Cisneros, 23—are still unaccounted for. Fifteen have either been ransomed or returned home. Though the border has long been plagued by drug-related crime, authorities blame the alarming surge of violence and disappearances on the Zetas, a heavily armed paramilitary group working for a powerful Mexican drug cartel, as well as copycat rival gangs. Though Mexico sent more than 600 soldiers and federal officers into Nuevo Laredo in early March to curb violence, fear of the Zetas is so strong that people who have been returned to their families will not discuss what happened to them. Even the U.S. State Department has warned travelers in the area to use caution. "The local and state police are outmanned, outgunned and outtrained," says Laredo FBI agent Art Fontes. "People are in fear of their lives."

Slemaker, for one, isn't letting that stop his hunt for Yvette, who left her two young daughters with a relative to cross the border to Nuevo Laredo, a city of some 500,000. Alerted by the babysitter that Yvette—the oldest of his five children—had not returned, Slemaker took a leave from work to turn detective, but got little cooperation from authorities. "They treated it like a joke," he says. Even when he found Yvette's abandoned sedan in Nuevo Laredo, he got little help in figuring out his daughter's fate. "My world has come to a standstill," says Maria Antonieta, 45, who has been caring for Yvette's daughters Icela, 6, and Daniela, 8, since their mother's disappearance.

Santiago Palmeros knows the feeling. The Nuevo Laredo radio news reporter's widowed niece Raquel threw a 4th-birthday party Nov. 28 for her son, then went for a drive with Palmeros's daughter Erica. "She would never leave without letting me know where she'd be," says Palmeros, 58. They were seen at a Nuevo Laredo club that night, but never returned.

Rosita Gonzalez, 51, has been waiting since Dec. 5 for word from her two sons, Gerardo, 24, and Samuel, 18, both day laborers, who left their homes in suburban Laredo that day to drive 110 miles to Monterrey, Mexico. The pair phoned that afternoon from what appeared to be an official checkpoint, but then vanished. Like many relatives of people who may be in the hands of the Zetas, Gonzalez was too scared to inform police. "I was afraid," she says, "that an organized crime group would come after me."

With good reason. The Zetas began in the 1990s as an army commando-like unit aimed at combating drug trafficking. But 30 to 40 of them turned renegade a few years ago, going to work for a drug gang known as the Gulf Cartel, whose enforcers they trained in military tactics. Clad in black uniforms, toting guns, they seem to control the streets of Nuevo Laredo. FBI sources believe the Zetas snatch victims for reasons that aren't always clear—including ransom, retribution and information on rivals.

And in these perilous times, even hunting for the missing can prove a risky business. Slemaker, however, has not shied away from drawing attention, posting signs and giving interviews. His forthrightness has turned him into a spokesman for all the families of the missing. "He knows how to express what we all want to say," says Rosita Gonzalez, the mother of the missing brothers.

Slemaker says speaking up is the only way to maintain hope that his daughter might return—a hope that he and Maria Antonieta have not given up. In a recurring dream, Maria Antonieta says Yvette returns and whispers in her ear, "Take care of my girls." When she wakes up she can feel Yvette's presence. "I talk out loud to her and say, 'Yes. I will take care of them,' " says Maria Antonieta, " 'but come home soon, because we miss you.' "

  • Contributors:
  • Anna Macias Aguayo,
  • Cary Cardwell,
  • Adrienne Bard.