Many sites have a lot of 1 or 101 rep users:
It's not abnormal to see a series of 101 rep users on a site. People will naturally become curious and check out the site, but they may not participate in the actual Q&A. They may actually just participate by reading the question and answers, voting, commenting, or suggesting edits, and this is fine. Most of a healthy site's traffic will come from search engines, and this means that a majority of the people reading the content here will not be registered users.
There are a few sites I participate on where I don't ask/answer, but I like reading the content. Not everyone is as involved as you guys and gals are, and we can't expect every single registered user to post.
Content is King:
With that said, GeneJ has the right idea. The secret to growth is sustained growth. As the content grows, as the number of good questions and answers grows, people doing searches on Google will find this site. But if the content isn't helpful, they won't stick around. Not saying that's happening here or that anyone is suggesting this. I'm just making a point for the benefit of all who happen upon this post.
Let's not spam SE Users:
I also don't support directly contacting everyone who has registered. If they like what is posted, and feel like they would fit into the community, then they'll post. But spamming people just isn't what Stack Exchange is about. This would only decrease the signal to noise ratio and make me less likely to register on new sites and check out the community.
I do think lkessler (I'm assuming you're the elusive Louis GeneJ refers to) has the right idea, blogging, tweeting, and getting the word out, via sharing interesting questions with people who are interested in the subject, is the right idea, but spamming existing Stack Exchange users doesn't seem right.
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