A small number of emigrants left for the USA (and other places) from the port of Stettin (today called Szczecin in Poland). The surviving passenger departure lists are available at the Vorpommersches Landesarchiv in Greifswald, Germany, and online at Ancestry.com.
Ancestry has digitized the Stettin passenger lists, along with passenger lists for the German port of Swinemünde (today called Swinoujscie in Poland), and put them online. They are not indexed, but can be browsed by time frame and port:
It is recommended that you write in German and include an IRC (International Reply Coupon).
More information about this archive and contact information can be found here (site is in German)...