From my experience, most of the Nicolaes I know (of any age, actually) go by
Nicu, the Romanian equivalent of
Nick.
But even in English speaking countries I'd expect most teenagers to put "
Nick LastName" on Facebook rather than "
Nicholas LastName". Same thing with Tom/Tommy over
Thomas and Fred/Freddie over
Frederick. Sometimes some full names can be seen as a little pretentious.
Just my observations :)