I also face the same problem..maybe you try
\usepackage{natbib}
and from [utmthesis-authordate.bst] you can choose the style you want .for example:
% \citet{key} ==>> Jones et al. (1990)
% \citet*{key} ==>> Jones, Baker, and Smith (1990)
% \citep{key} ==>> (Jones et al., 1990)
% \citep*{key} ==>> (Jones, Baker, and Smith, 1990)
% \citep[chap. 2]{key} ==>> (Jones et al., 1990, chap. 2)
% \citep[e.g.][]{key} ==>> (e.g. Jones et al., 1990)
% \citep[e.g.][p. 32]{key} ==>> (e.g. Jones et al., p. 32)
% \citeauthor{key} ==>> Jones et al.
% \citeauthor*{key} ==>> Jones, Baker, and Smith
% \citeyear{key} ==>> 1990
Hope it works..