Probably, you have heard "사귈레?"(sagilrae?). But it doesn't mean "Wanna date ?", it is more like "Can you be my girl(boy) friend ?" in a informal way. If you want to say "Wanna date ?", use this one "데이트할레?"(date halre?). That is "Wanna date ?" in a informal way.

우리 사귈래?