well if you don't remember them they can't really be your friends because there not important enough for you to remember.
just do things for you best friends. the ones who have known you the longest. those who have always been there. those who have always been the best. those who are special.
really if you don't remember them. i wouldn't call them friends. not saying they aren't nice people who you enjoy being with. because i enjoy talking with anyone. i think it's great.
anyway you don't want to end up drawing 100 pictures so i would just make them for the special people. either way if you made them for random watchers or friends people will miss out. it's hard to serve all.
i would do it for friends because it makes it special that you coninue to express how much they are to you. i'm sure it will feel nicer to draw for people who are important to you.