  In the present investigation, we study the class of Sigmoid starlike
functions, given by $\mathcal{S}^*_{SG}=\{f\in\mathcal{A}: {zf'(z)}/{f(z)}\prec
2/(1+e^{-z})\}$ in context of estimating the sharp radius constants associated
with several known subclasses of starlike functions. Further, graphical
validation for the sharpness of results is also provided.
