Yes, you do, but the problem is in the inference.
If you tell someone not to partake in the census, you are inviting them not to, as if it were a nasty thing (which is not, of course)
I suggest "No particiPAR en el censo" so as to make it a proper call-to-action.
it's in the infinitive, just like in English, instead of present simple, which sounds like a smooth invitation.
TL;DR
By saying "No participes en el censo", you are not calling to action, but advising the user what to avoid. It sounds really, really awkward.
Spanish is my mother tongue. I know what I'm talking about.
Best,
David