Emacs Auctex custom syntax highlight

I'd like to highlight a new command I created in LaTeX:

\newcommand{\conceito}[3]{
  \subsection{#1} (Original: \textit{#2} #3).
}

I use this code in this way:

\conceito{Foo}{Bar}{Bla}

I followed the manual and put this code in my ~/.emacs, but it didn't work:

(add-hook 'LaTeX-mode-hook
    (lambda ()
        (font-lock-add-keywords nil
          '((""\\<\\(\\conceito)\\>"" 1 font-lock-warning-face t)))))

What's wrong?