HALVORSEN/VAARE 1855

I am trying to find Ole Andreas Halvorsen (Farm name Vaare) 25 years old who left for "Nord-Amerika" 20.4.1855. This record is from the Passport records for the bailiff in Ryfylke 1811-1859. I'm guessing he left thru Christiana. He wound up in Illinois and changed his last name to "Warren". Go figure. Any help in searching passenger lists would be appreciated. thank you Jennifer