There are different ways of getting an erotic massage in Santiago. Massage parlours are one very common way, though be aware that some of them are straight-up brothels. You can find those places in apartments around Santiago. You’d best ask around, or look for ads in newspapers. There are few that advertise online like the Amazon Spa (http://www.amazonaspa.cl/) at Av. Manquehue Sur. Santiago de ChileLa Mansion Del Masaje (http://www.lamansiondelmasaje.cl/) is one of the super-secret ones that don’t give you an address right away. $100 will get you a 4-hands massage, which is a bargain.
In case you would like to book an independent masseuse you can browse local directory sites for ads and profiles of individual girls offering masajes eróticos. Note that many masseuses can be tied to a salon or escorts service. So in reality they are not always really independent but that does not mean they cannot deliver a good massage service.
Saunas are another option when you are looking around for a decent rub and tug in Santiago. Try for instance Sauna Mi Tiempo (http://saunamitiempo.cl/) at Bombero Núñez 230. There are many more, just pay attention that many are run by and targeting the gay community. So better ask in advance if that’s not your thing.