I have tried searching some genealogies and I couldn´t find any of my ancestors there.
Maybe it's as simple as the fact that nobody has uploaded anything relating to your family. Apart from what I've added myself, I can find little relating to my family branches, either. I was rather more fortunate when I used Ancestry Trees, although the accuracy of the content was rather questionable.
I assume you were checking here:
Note that these are based on uploaded GEDCOM files from numerous submitters - each in a private - disjoint set of records.
HOWEVER the MAIN collaborative family tree database is not there
but is here: (the FAMILY TREE)
did you check there?
BOTH of these areas of FamilySearch are based on user submitted data
so as Paul pointed out - these databases are only as good as what info has been submitted by users like you.
also check out: