This discussion is an extension of this answer but in Beamer -documentclass and with XeLaTeX. I can get some variants working there in Pdflatex, see Christian's answer but with bad output and I do not want it, since I lose the nice layout what XeLaTeX can offer.
Code based on egreg's answer and which I think offers the best extensibility to solve this problem here in XeLaTeX
\documentclass{beamer}
\usepackage[T1]{fontenc}
\usepackage{newunicodechar}
\begin{document}
\begin{titlepage}
š
\end{titlepage}
\end{document}
Any options offered in the above discussion are not working XeLaTeX.
Output nothing.

beamerused? Please, make an example that really reflects what you want. – egreg Feb 26 '15 at 15:17\v{s}again? – Werner Feb 26 '15 at 15:38