Informal:
* Hola, chica: This is the most literal translation, but it's a bit more formal than "Hey girl."
* Oye, chica: This is more informal and friendly.
* Hola, guapa: This means "Hello, beautiful." It's more flirtatious than the other options.
* Hey, linda: This is a more casual and friendly way to say "Hey, pretty."
Formal:
* Hola, señorita: This is the most formal option, and it's best used when addressing someone you don't know well.
* Hola, joven: This means "Hello, young lady" and is also a more formal option.
Other options:
* Guapísima: This is a very affectionate and playful way to say "Hey girl" and is often used between friends.
* Chica: This is a very simple and casual way to address a girl, similar to "girl" in English.
The best option for you will depend on the context of the situation and your relationship with the person.