Some 40,000 people have gone missing since the start of the country's drug war in 2006. Very few have ever been found, though clandestine mass graves dot the countryside. Often, human remains are not identified, leaving some families with no word of their loved ones for more than a decade.
That is the case for Rocío Morales, whose son was kidnapped almost 11 years ago. She wept quietly, but desperately at the Mexico City march as she held up a banner with a photo of Pedro Morales González. The banner was made five years ago to mark the anniversary of his disappearance and she has been marching with it ever since.
Though Morales has filed crime reports with local, state and federal police and gone from agency and agency looking for information, she said, "There has been nothing, nothing, even though I know who did it." Too poor to hire a lawyer, she said authorities "just close the door in our face."
"I want to know what happened to him," said Morales, who is raising the children of her son, who was a 37-year-old electrical company employee. "This is not life, this is like a living death, not knowing where our children are."
Hundreds of other mothers marched in the Gulf coast state of Veracruz and the northern cities of Monterrey and Ciudad Victoria, chanting: "They took them alive, we want them back alive!" and "Why do we search for them? Because we love them!"
The mothers are often looking for a police report, forensic investigation or just a bit of bone to help them understand what happened. Such marches also serve as a way for women to support each other and remind their children they are not forgotten.
"Children, listen, your mother is still fighting," they chanted in Mexico City.