I had looked into this once before, but never indulged myself. The following info is about a year old and is second hand, so the usual caveats apply. Someone I knew recommended this site for outcalls:

http://escortprivada.com/escorts/lisbon/

However the women he specifically met and praised are no longer advertised there. The following is either an incall agency or some sort of brothel:

http://www.michelleeassistentes.com/

Like I said I have never tried any of these or even been to Portugal, but if you just need a few leads there you go.

Portalprivado.  Apartadox.  Gallery club