How should I publicly announce a new ruby stone?
You can create a thread on the official ruby forums as well as forums / blogs that post information about Ruby and any website related to the gem you create.
To be honest, I don't think you need to advertise a gem much, usually when I want to search for a gem, I just put whatever I want to search in the search bar, so make sure your gem shows up if people have it.
source to share
In addition to what @ T.Aoukar already suggested, you can also try #rubyonrails
on irc.freenode.net
and any Ruby mailing lists that might be relevant. Make sure you check their policies first, but everything should be fine.
Another good way to promote your gem is to talk to a local or regional ruby (I really hope there is one in your area. If not, maybe you can start one?) And to the Weak Channel community or similar.
Many Rubyists are also very active on social media such as Twitter. This gives you another channel to look for feedback and promotion.
source to share