Lost reletive

Hello. This is the first time I try to find a relative this way. I am looking for a half brother of my grandmother. His name is Kristoffer Olsen born 10 of dec 1886 in Nötteröy Norway. His mothers name Josefine Hansdatter Myhre, fathers name Kristoffer Hansen.(They were not married).Her first husband (my grandmothers father Andreas Olsen) When she married the second time in 1906 Kristoffer dicided to leave because he could not like his new "father". He went to America and he sent two postcards to his mother and after that nothing. I have been looking in different pages on the internet but I can not find him. If there are someone who know something about him I whould be very thankful. Goran