Hi, What research have you already done - Perhaps Obituries for your Grandparent/s - may mention other connected family.
Have you posted to Infoukes Genealogy.?
You might find some help there - list members are very helful - some very knowledgeable.
It is a Mail List -
Address a request to subscribe to the followingGenealogyfirstname.lastname@example.org
On the Subject Line - type only the word - Subscribe
In the Body of the Message - type only the word -Subscribe
When you receive your welcome message - you will then be able to post your message - and hopefully find some connected family members.
Have you searched Passenger Lists - may show family members who had travelled together.
Citizenship: Have you obtained Citizenship papers for your grandfather - this may show the names of his parents including the mothers maiden name etc
Have you searched US. Census -You might find other family members.