The extremum seeking control (ESC) is a model free approach for solving the online optimization control problems. In this paper, a general purpose ESC based on the fractional order sliding mode is presented with a suitable application on the plasma impedance matching. The principle and stability of the proposed control law are illustrated mathematically. Simulation is provided to show the effectiveness, necessity and worthiness of using this advanced control strategy. Remarks are given with regard to the implementation and potential research opportunities.