Lost soul = a person who does not seem to know what to do = 途方(とほう)に 暮(く)れた人(ひと) Rather hard to explain, just remember please.....

失われた魂 うしなわれたたましい This is my take on it.

Maybe something like 迷った魂 but that is quite literal. I don't know how to translate it naturally. I think a lost soul means eternally wandering, right?