Maybe you should put aside the search for purpose as such. Instead, I suggest you address the problem of fear you mentioned in your post. In what sense are you afraid to fail? Is it fear of people not liking your work? Or that you may start and not finish it? Or that you cannot make a living from it?
You should realize that whatever the answer, it makes no sense to get worried. If the situation is out of your control, it is pointless to care about; if you can control it, go and do something about it. Worrying is not gonna get you closer to the solution.
If writing is what you love, but you are afraid or stuck, I suggest you try some freewriting. Write for ten minutes, non-stop and without erasing (forget about spelling or grammar), whatever you have on your mind. If you have nothing to write, repeat a sentence like " I have nothing to write, I have nothing to write....". This is just to get you started. If after the ten minute period you fell like keep going, do it. Do this exercise everyday for at least two weeks (I'll suggest 30 days to install the habit).
Once you become loose, you should write with some ideas for your play. A background story, a character description, the message or theme you want to address, etc. The idea is get you writing.
Finally, I suggest you read "10 secrets for success and inner peace" by Wayne Dyer. It can light your mood get you moving.