Colombian police are investigating the killings of three youths whose names appeared on hitlists published on the social networking site Facebook.
The hitlists warned scores of teenagers in the town of Puerto Asis, in southern Colombia, to leave town or be killed.
Two of the youths named were shot on 15 August, while a third was killed five days later.
Police have sent an investigative team, including internet experts, to find out who is behind the threats.
A local official said a criminal gang had recently expanded its operations to the area and was intimidating locals.
Diego Ferney Jaramillo, 16, and Eibart Alejandro Ruiz Munoz, 17, were shot dead as they were driving along a road on the outskirts of Puerto Asis in Putumayo province on their motorcycle on 15 August.
Colombian ombudsman Volmar Perez Ortiz said that at around the same time, anonymous threats appeared on Facebook, listing 69 local youths and telling them to leave Puerto Asis within three days or be killed.
Panic and fear
The names of the two dead teenagers had been on the list. The ombudsman's office said the authorities at first thought they were dealing with a hoax.
But the killing of a third listed teenager, Norbey Alexander Vargas, on 20 August prompted officials to take the threats seriously.
Since then, a second threat has appeared, on leaflets left on cars and addressed to the families of the youths.
"Please, as relatives, ask them to leave town in less than three days, or we'll see ourselves forced to carry out more acts like that of 15 August," it read.
Another list was published on Facebook on Monday, this time naming 31 local girls.
Putumayo province official Andres Gerardo Verdugo said the threats had provoked panic among the town's families, some of whom had fled.
Police officials have not yet commented on who may be behind the threats or why the youths had been targeted.
But the ombudsman's office said a notorious gang, the Rastrojos, had recently stepped up its criminal operations in the area.