Automatic Indexing of Citations using natbib

Question

I'm using the natbib package with imakeidx to generate a list of citations using \citeindextrue as follows

\documentclass{article}
\usepackage{natbib}
\usepackages{imakeidx}

\makeindex
\begin{document}
    \citeindextrue
    \citet{Knuth}
    \citep{Knuth}
% Bibliography is manually generated
    \begin{thebibliography}{000}
       \bibitem[Donald~E. Knuth(1986)]{Knuth} \newblock \emph{The {\TeX}book}, volume~A of           
       \emph{Computers and Typesetting}. Addison-Wesley, Reading, MA, USA, 1986.
    \end{thebibliography}
    \printindex
\end{document}

but when running nothing is typeset in the output file, I want to know if I'm missing something or maybe this method doesn't work with thebibliography environment.