Mass sensing and time keeping applications require high frequency integrated micromechanical oscillators. To overcome the increasing mechanical stiffness of these structures sensitive optical vibration detection and efficient actuation is required. Therefore we have implemented an active feedback system, where the feedback signal is provided by the optical gradient force that is present between nanophotonic waveguides on a silicon-on-insulator chip. We found that access to the parametric instability regime can be easily controlled by tuning the wavelength.