양(孃) is a dependent noun(의존명사) which is used after a name of woman as an honorific title for a girl or young woman. Similarly, 군(君) is used for a young man but it is less commonly used than 양.

yeah, -양 is used for calling a female listener's name; usually someone seems younger than you or even a kid. So, I would say it's like 'Miss' and 'madmoiselle'. But if you want to use '-씨' in some formal cases, that's fine. cf. for male listeners, you use '-군'(for younger boys) and '-씨' (same as above).