  A Dalitz plot analysis of the OZI rule violating decay $D^+_s$ into $\pi^-
\pi^+ \pi^+$ is presented using different partial wave approaches. Scalar and
vector waves are described by $K$-matrices; their production is parameterized
in a $P$-vector approach. Alternatively, Breit-Wigner amplitudes and Flatt\'e
parametrization are used. Special emphasis is devoted to scalar mesons. The
$f_0(980)$ resonance provides the most significant contribution. Adding
$f_0(1500)$ to the scalar wave leads to an acceptable fit while introduction of
$f_0(1370)$ and/or $f_0(1710)$ does not lead to significant improvements. A
scan of the scalar wave optimizes for $M=1452\pm 22$ MeV/c$^2$. When
$f_0(1710)$ is added, the mass uncertainty increases, and the fit yields
$M=1470\pm 60$ MeV/c$^2$ which is fully compatible with the nominal $f_0(1500)$
mass. The scalar wave seems to exhibit a phase motion of 270$^{\circ}$ units in
the mass range from 1200 to 1650 MeV/c$^2$.
