In terms of grammar, "말아요" is often used in everyday Korean, but it's not standard.:(
The base form of it is "말다", and it conjugates like...
1. 마 e.g. 가지 마! (Don't go/leave)
2. 마요 (polite form) e.g. Please don't leave/go
3. 마라 e.g. 말다 + 아/어 라 > 마라 (I want you not to go/leave)
\^o^/