The latest arrest in the grisly crime puts the final suspect in the case behind bars, said the southwestern state's attorney general Martha Elva Garzon.
She declined to give the suspect's name or age, but said he was being held at a special center for teenagers in Chilpancingo, the state capital.
In addition to rape, he may be charged with theft and conspiracy, Garzon added.
Gunmen wearing masks burst into a beach bungalow where 14 tourists were staying on February 4th, tying up seven Spanish men and raping the six Spanish women, while sparing a Mexican woman.
Six men, including two minors, were detained just days after the brutal attack. Mexican Attorney General Jesus Murillo Karam told reporters at the time that the suspects had "confessed to everything".
Mexico has sought to clean up its image as a violent country in order to convince tourists to keep coming, despite having seen more than 70,000 drug-related deaths since 2006.
Acapulco has seen its share of drug violence, with gangs dumping the bodies and heads of rivals in the street. It still attracts nine million visitors a year, though only a third are foreigners.
The assault further tarnished the reputation of the Pacific port city, a once glitzy haunt of Hollywood stars such as Frank Sinatra and Elizabeth Taylor beset by violence in recent years.