Heroku Procfile not working

I'm trying use Nginx + Phalcon. So I have the root folder (app) and my public folder (app/public).

Inside the root (app) I have the Procfile:

web: vendor/bin/heroku-php-nginx -C nginx_app.conf public/

And inside my public folder I have my index.php

<?php exit('hello');

With this simple example, shouldn't print hello when I access the url myapp.herokuapp.com?

If my thought is right, which is not working. My second problem is that the nginx_app.conf seems that are not been reading by the server. Because every f* page that I tried access I got 404.

So, what am I doing wrong?

[UPDATED]

Here's the log:

heroku[web.1]: State changed from down to starting
heroku[web.1]: Starting process with command `php -S 0.0.0.0:57262`
heroku[web.1]: State changed from starting to up
app[web.1]: [Tue Apr  7 11:08:07 2015] 10.185.81.31:28258 Invalid request (Unexpected EOF)
app[web.1]: [Tue Apr  7 11:08:07 2015] 172.19.28.141:33686 Invalid request (Unexpected EOF)
heroku[router]: at=info method=GET path="/" host=myapp.herokuapp.com request_id=d39f119a-fd95-4887-809f-74712925606f fwd="200.221.158.131" dyno=web.1 connect=2ms service=4ms status=404 bytes=668
app[web.1]: [Tue Apr  7 11:08:44 2015] 10.61.196.230:38679 [404]: / - No such file or directory

[UPDATED]

$ git push ...
[...]
remote: -----> Discovering process types
remote:        Procfile declares types -> web

$ heroku run bash
$ cat Procfile
~ $ : vendor/bin/heroku-php-nginx public/~ $

And according the documentation should be

heroku run bash
Running `bash` attached to terminal... up, run.5662
$ cat Procfile
web: vendor/bin/heroku-php-apache2

A little detail that I have tried:

cat Procfile
~ $ vendor/bin/heroku-php-nginx public/c/~ $
vendor/bin/heroku-php-nginx public/
DOCUMENT_ROOT changed to 'public/'
Optimzing defaults for 1X dyno...
4 processes at 128MB memory limit.
Starting php-fpm...
Starting nginx...

I'm waiting... let's see what happens