Simulating Multiple Feedback Low Pass filter using LTSPICE
This tutorial has a good overview of sweeps in LTSpice.

To summarize: Give your voltage source the value AC 1 (where you currently have 1V for a DC source), and the sweep will take care of setting the frequency.  

Add a .ac directive, either by using the S shortcut key and typing the Spice directive (The format is .ac [oct|dec|lin] [step size] [start frequency] [stop frequency], where dec/oct/lin refer to a decade, octave, or linear sweep rate) or through the Simulate->Edit Simulation Command menu. 

That tutorial also talks about sweeping parameter values to simultaneously plot the response with various capacitor and resistor values with the .param and .step directive.  These two tools together are very useful when designing a filter.