# totally untested! again
my $users = $nt->lookup_users; 
foreach my $usr (@$users){

   print $usr{screen_name}; #??
   use Data:Dump dd method to see the structure you get back (better than Data::Dumper)
   dd $usr
}
# or directly first element returned
print $$users[0]->{screen_name};
dd $$users[0];