-men们 can be put after nouns which contain human being, since the radical of the character 们relates 人ren2 human. We can say: wǒmen(we)， nǐmen(you)， tāmen(they), lǎoshīmen(teachers)，pénɡyoumen(friends),etc. However, the plural form is not an important thing. When the plural form is not necessary or other words give the idea of plural, plural form is normally omitted. For example: wǒ xiǎnɡ ɡēn wǒ de pénɡyou qù tú shū ɡuǎn。(It's not clear I will go to the library with a friend or friends. ) wǒ xiǎnɡ ɡēn wǒ de pénɡyoumen qù tú shū ɡuǎn。( It's very clear I will go to the library with my friendS.) Actually people don't care you will go with one or more friends, so the first sentence is more popular. wǒ yǒu sān ɡè zhōnɡ ɡuó pénɡyou 。 (I have three Chinese friends.) Since there is sān ɡè (three) to indicate plural, we can't put men们after pénɡyou. More details you can check some grammar book.

Hi,Luis yes,it functions as a general plural marker, and I think it can be used for every "thing":human,animals,things(just we don't use "-men"after things often,but it's right) For example: we----wo3 men they---ta1 men men---nan2 ren2 men women---nv3 ren2 men monkeies---hou2 zi men Anna

yes! but most of case is related with human, sometime it could be used for animal but only take them have human mind. nv3 hai2 :girl nv3 hai2 men2: girls