\documentclass[12pt]{report}

% Defining new counters
\newcounter{author}

% Defining Author Macros
\def\coun{$^{\arabic{author}}$%
\addtocounter{author}{1}
}

\def\AddAuthor#1#2{
\ifdefined\Authors
         \xdef\Authors{\Authors, #1\coun}
\else
         \gdef\Authors{#1\coun}
\fi
}


\begin{document}

\setcounter{author}{1}

\AddAuthor{A. Yaghoubi}{}
\AddAuthor{H. Nehzati}{asdf}
\AddAuthor{S. Gehibi}{Gheibi}
\AddAuthor{Farschad Torabi}{Somewhere in the world}

\Authors


\end{document}