As assuming you are using traditional exp/imp, you need to create user manually. It will not get created automatically.
Even old style export will create user/roles for you but only if you do a 'full' import. Can you post your export/import commands so we can see what is going wrong and the log rom your import where you get problems.
exp system/(password) FULL=Y FILE=(exp-file)
imp system/(password) FULL=Y FILE=(exp-file)
That should work OK - i can only think there was a problem with the tablespaces getting created, so then the users failed to create and had a knock on effect in the rest of the export.
Can you paste the fist 50 lines or so of the import logfile?
Ugh, I found the answer. The person that created the new blank DB named it differently and that was throwing the IMP off. I recreated the DB with the same name and now it's working.