We have a facebook group for all Erasmus students that are or will be studying in the Polytechnic University of Catalonia and are looking for accommodation: 

https://www.facebook.com/groups/1639257629645502/?ref=share

Moreover, we have a special partner for accommodation, Badi.In Badi you can find your ideal roommates with whom to share your Erasmus experience. Safe, flexible and transparent, Badi offers you a wide selection of rooms and roommates for a unique experience. Check their website: http://badi.link/esnspain