To ask for help, you would typically use a phrase like:
* Помози ми! (Pomozi mi!) - Help me! (informal, singular "you")
* Помозите ми! (Pomozite mi!) - Help me! (formal, plural "you" or singular formal "you")
* Треба ми помоћ! (Treba mi pomoć!) - I need help!
The best choice depends on the context and your relationship with the person you're asking.