There is this support page
http://www.facebook.com/SupportLukaMagnotta
A lot of the members seem to be people against him anyway though.
As for him being mentally ill, I really don't think he is schizophrenic or anything like that. I read an article from the psychiatrist of Paul Bernardo where he stated (paraphrasing) that he felt this guy's act was far too meticulous and also suggested that mentally ill people don't have the tendency to commit murder in a sexually motivated fashion, where that appeared to be the case here.