How do you know anyone has even taken up your suggestion to be able to say it seems not to have worked, e.g. what hasn't worked ?
People have to presumably either have checked out your facebook profile/wall or posts, etc. Sorry I don't know the correct terminology, I flatly refuse to sign up to any social networking site. Then they would have to click the link to download avast, next they must install it and then register it. It is only that that point having registered avast that your account would be credited with your recommendation.