Voldemort can cast a curse that alerts his Death Eaters whenever his name is spoken. The order of Phoenix knows that later on. For example in volume 7, chapter 11 after Harry, Ron and Hermione escape from the wedding:
They explained what had happened; when they had finished, Lupin looked aghast. “But how did they find you so quickly? It’s impossible to track anyone who Apparates, unless you grab hold of them as they disappear!”
So I am curious why he didn't cast it on Harry Potter's name so he could track down Harry Potter while the Order hasn't recognized it.