I think it's okay to stop contacting people if you feel like you are making more effort than they are or if you worry that they are not interested in being friends.

Their response or lack of response can have less to do with you than it has to do with them. They may not be in a position to be friends with you now, but it may or may not mean that they don't want to be your friend. Like other people said, they may have other stuff going on.