I was told that my question involving recruiting librarians from their site to join the Area51 proposed Genealogy site was an inappropriate question. Many librarians are excellent researchers and I thought it was a perfect fit and suggestion. Is there a better place within StackExchange to attract members with over 200 reputation to an Area51 proposal?
Based on my comments with bfavaretto, you can probably tell I'm not a fan of spamming existing Stack Exchange users, at least not on this platform.
While I have occasionally mentioned in chat that there's a [insert my proposal here] site on Area 51, I generally try to respect everyone's space. If the topic of Motorcycles comes up in chat, I am sure to casually mention the site. Other than that, there's not much else to do.
My user profile on The Workplace does list some sites I've proposed that I'm interested in promoting. I've seen a few Workplace people follow my proposals, which suggests I should consider copying that profile to other sites I participate on, as the test is clearly successful.
Note that earlier you asked me if you could remove Stack Overflow from your list of sites, since you didn't mean to create an account there. Well, consider that one of the ways to promote your site is to participate in other Stack Exchange sites and write good quality questions and answers. If people notice you, they will check out your profile. Put a photo up too. The more interesting you look, the more likely people will check out your profile.
Lastly, look at profiles of interesting people on the Libraries site. Do they list a Twitter or Facebook account? If so, be sure to follow them. When you use those social networking tools to reach out to all your followers, you can include the Stack Exchange folks as a side benefit of promoting outside the Stack Exchange family. In short, you can reach BOTH existing Stack Exchange users as well as people who have not heard of Stack Exchange. Hope this helps!
As an aside, the Genealogy proposal now has 75% committment. It was proposed only 1 month ago. This could be the fastest proposal-to-private-beta in Stack Exchange history!
I've been thinking about that too, and it seems the only place where that would be acceptable is chat, since comments and answers are supposed to stay on-topic.
Other than that, Area 51 encourages users to "spread the word" by email or social networks only – which, I agree, is not the ideal way to target other StackExchange members.