Well, maybe not a "good" source, but these are my two cents: I study Electrical Engineering in Madrid's Technical School and I often check my e-mail in a hall where there are several computers for students. I don't use Tuenti but every single day I hear conversations about someone's pics on Tuenti, and every single day there are people next to me checking someone up on Tuenti. Tuenti is definitely more popular than Facebook in Madrid's universities.