The Spanish pronouns "quién" and "quiénes" (who, whom), can only be used to refer to people.

*they can be used as Interrogative pronouns:

¿Quién habla? - Who is speaking?
¿Quién llamó a la policía? - Who called the police?
¿Quiénes son ustedes? - Who are you?

*after a a preposition:

¿A quién viene a ver? - Whom are you here to see?
¿A quiénes pediste un favor? - Whom did you ask a favor to?
¿De quién es el libro? - Whose book is this?
¿De quiénes son estos juguetes? - Whose toys are these?

*they can also be used as Relative pronouns

El que fue ayer fue quien lo hizo.
He who went yesterday did it.
Las mujeres de quienes hablo son españolas.
The women of whom I speak about are Spanish.
La señorita a quien esperabas acaba de llegar.
The girl whom you were expecting just arrived.

Sentences with "quién"
Sentences with "quiénes"