We construct explicit examples of Frostman-type measures concentrated on arbitrary planar rectifiable curves of positive length. Based on such constructions we obtain for each $p in (1,infty)$ an exact description of the trace space of the first-order Sobolev space $W^{1}_{p}(mathbb{R}^{2})$ to an arbitrary planar rectifiable curve $Gamma subset mathbb{R}^{2}$ of positive length.