"We're in a war," Moreno told a news conference late on Monday. "We're in a constant battle."
Moreno said at least three of the victims were teenagers. He said the federal attorney general's office has taken over the investigation.
Minutes after the grisly discovery, four other bodies were found in another empty lot in Tijuana, and two other bodies were discovered late on Sunday in a lot next to a factory.
Investigators believe 16 of the victims were killed by warring drug gangs. The other two were victims of street crime, an official said.
Tijuana is among the cities hardest hit by violence as Mexico's drug cartels battle for lucrative smuggling routes past the border to supply illegal drug users in the United States.