Convoys carrying the families arrived in Mexico City on Thursday after touring the country to rally support.
|Masked protesters clashed with police near the airport hours before the three |
marches started. Some 200 hooded protesters threw rocks and Molotov cocktails
at police officers burning a motorcycle.
Francisco Lagro, father of 19-year-old Magdaleno, one of those missing, was travelling on one of the caravans.
"It's been almost two months without knowing where they are. We don't know anything and we're desperate," he said.
"What are they doing? In what conditions? Do they get any water or food? Are they tied up? We have so many questions."
|The government's handling of the case of the missing students |
has provoked widespread anger in Mexico
A small protest turned violent near Mexico City's international airport, when some 200 hooded protesters threw rocks and Molotov cocktails at police officers who had been trying to disperse them. Police say no-one was injured.
Despite that incident, the protests were less violent and destructive than those just over a week ago.
Many shops and businesses were reportedly closed on Thursday because of the marches.
|Bolivian students marched in solidarity with their Mexican counterparts in La Paz|
The abduction has galvanised opposition to rampant political corruption and violence, says the BBC's Wyre Davies in Mexico City.
Mexican President Enrique Pena Nieto has accused some of the protesters of trying to "destabilise" the state.
|A student takes part in a protest by students of the Ayotzinapa school|
and parents of the 43 missing students in Acapulco
The protests for the missing students reflect wider anger at political corruption
The students, all trainee teachers, went missing after attending a protest in Iguala, Guerrero State.
Forensic tests are being carried out on bodies found in mass graves in the state.
More than 100,000 people have been killed and 27,000 have disappeared in Mexico in the last decade.