Is it rude to call an unknown people in japan with "Oneechan" or "Oniichan" calling?

Question:

For example, I need some help about the location of a place, so I ask the nearest school girl (younger than me) with "Sumimasen Oneechan ... tasukete kudasaimasen ka" .... or something like that. And how to say "Excuse me officer .." in Japan (for example if I need a help from a police officer).

Answer:

It is not always rude but you better to be careful because it could be harassment. It depends on situation.
It is actually very casual. I mean it is ok but it is not acceptable some situation.

e.g.
If I am a waitress at coffe shop, customer (kids and elder people) calle me 'Oneechan' to order something, I wouldn’t mind their language but everyone is different.
Some girls might think you are rude and not polite.

To police officer,
I wouldn’t use these words. If I need their help, I just say ‘ sumimasen ( I know it means sorry but in this situation, the meaning is Excuse me. )