I'm afraid you seem to confuse them,peng you men (朋友们) just means friends,peng you（朋友） means friend.I hope my answer can do some help.^~^

朋友们 --- is the way of addressing

wow,I have to say it also confuses me as well,even I was Chinese.I even haven't noticed that before. literally 朋友=friend 朋友们=friends. Thomas and his friend托马斯和他的朋友 Thomas and his friends托马斯和他的朋友们（mostly it is a movie name or a book name ) He is my friend.他是我的朋友 They are my friends.他们是我的朋友。(we barely say 朋友们 here.) If you have better idea,please feel free to let me know.Vice versa