Do you subscribe to Ancestry.com? If not, you can go to the free Ellis Island website and find Paul RAAB's ship manifest entering the U.S. on the ship Kroonnland on September 11, 1906.
Included is his last place of residence and the name of the person he is traveling to join. This would be a good place for you to start your research.http://ellisisland.org/
His listed age was 16 when he entered the U.S. in 1906, making his birth date about 1890 in Germany. Knowing from the ship list that he was joining his aunt in St. Louis, Missouri, we can find his World War 1 draft registration card:
St. Louis, Missouri, June 5, 1917
Paul J. Rabb [his signature gave the correct spelling of RAAB], age 28
address: 6942 Manchester, St. Louis, MO
birth date: December 8, 1889
where were you born: Steinbach, Germany.
occupation: cane maker [looks as though it says core maker]
by whom employed: Scullen? [can't read well] Gallagher
supporting: wife and three children
married, caucasian, no prior military service
medium height, medium build, brown eyes, dark hair, not bald.