I do think it depends on your relationship with the person. So for like family and close friends I take a much more tentative approach. But for the most part, I continue to call people until they give a clear "No." In order to do that well, I have to be faithful at clarifying the "No" and asking if it "makes sense to follow up in (insert time amount here)?" All this is with the assumption that I am prioritizing "fresher" contacts and have the time to call unresponsive folks. Caveat: if you find that you are harboring negative thoughts/feelings toward that person as a result of the persistent follow up, maybe take a break and come back later when you can take joy in simply being faithful in the follow up.
For better or worse, I think this helps people learn to say "No" and helps me to press through insecurities. I understand it might annoy some people, but unless they have communicated they are not interested, who am I to assume that is their desire?
For what it's worth, I wouldn't say that I have necessarily seen an increase in responsiveness due to this approach. However, when I take this approach, I have very rarely felt that I let my insecurities keep me from being faithful to follow up anyone.