To clarify, I think it's jumping the gun quite a bit to say it's not working.
What is happening is that some people had started singing "You Are My Sunshine" to help comfort Natalie, and Roivas told us she could hear the music floating through the Dark Place and was following it in the hopes it would lead her to Natalie. However, she has not yet found Natalie.
This could be due to a number of things, one of which being that it isn't being sung often enough, and it only floats through the Dark Place once a week or so. Which, if that's the case, would imply we need to sing it more. However, there was also another theory put forward that Natalie is frightened by the music due to the puppets and Slenderman using it to scare her/draw her into danger, and is running away from it, making it harder for Roivas to find her. So an idea was put forward to read her children's stories as well, because that is something she won't run from.
We have no proof that the stories will work the same way as the music, we also have no proof that the music has stopped working. BUT, there doesn't seem to be any reason why story-reading would hurt so I think it's a good idea to try it as well. Just remember to help sing, too, because that's the only thing we have heard so far from a plot-character can actually be heard.