Should I play along?

I wouldn't, an Anonymous letter really doesn't do much. If you really like him try hanging out with him more often, drop subtle hints that your into him and see if a something blossoms. :)

Trust me, I've done the anonymous note thing. It doesn't really work...like at all. Unless you put your name on the note, it doesn't really have an effect on anyone. Either put your name on another note or even better go up to the person and hand it to them. It does take a lot but you can just talk to the guy too.The more personal you make it, the better effect it has.

I think this time you should confront him with another note and be cute about it lol.

I've learned the hard way that if you keep them in the "like" category and just beat around the bush when it comes to socializing with said person, you will not ever have a relationship with them. They will only see the awkward moments that you have when you are close to them. They do not know that you think about them daily or that you draw little hearts around your names. The only way to make something of it is to actually break from your shell, I did and I have not regretted one single moment. I missed out on a lot when I held back. Now, I will not miss an opportunity to shine. Good luck!