I would say "compared to the previous year". A native speaker would understand you either way, but I believe "compared to" is more grammatically correct.

Compared to previous year I would say is more common. However, both are understandable and if you want to say either, you must insert the definite article 'the' so it would be compared to THE previous year and compared with THE previous year.

I believe that "compare to" = to liken A to B: Mother (angry): You are just like your brother. Tommy (angry): Stop comparing me TO my brother. We are NOT alike. ***** To compare with = to show how 2 things are the same and how they are different How would you compare Mars with Jupiter? How would you compare a cat with a dog? THEREFORE, I think that people on December 30 will compare 2013 WITH 2012.

"Compared with previous years" (When talking about more than one year, you put an 's' at the end) :) *edit* though if you are just referring to the one year then "compared to the previous year" is correct, as the lady above me stated! :)