We numerically investigate the influence of sinusoidal flow control on the von Kármán vortex shedding behind a circular cylinder in two-dimensional flow. Actuator location, direction, frequency, and amplitude are varied to examine their effects on the wake and the corresponding change in drag on the cylinder. We place focus on the conditions for which the cylinder wake locks onto the actuation frequency. The lock-on region is found to be consistent with stability horns observed in oscillator dynamics. Under certain conditions, the actuation reduces drag by elongating the wake structure to appear more streamlined than the wake without flow control. In other cases, the use of actuation led to less streamlined wakes, resulting in no significant drag reduction or for some instances in a drag increase. Purely steady and oscillatory actuation components are examined to highlight their individual influence on the lock-on and drag characteristics. We also note that low frequency oscillations are observed for cases in the neighborhood of the lock-on boundaries due to the competition between low and high-drag states.