Olivia,
But how would a person without an account request membership?
Either with the email +subscribe command (listed on the group's home page), or by clicking the "Join This Group" button on the group's home page.
If they use the email command they are not required create a password (account) at groups.io. If they use the web button they'll be prompted to create one.
I'm worried about future new members being able to find the group and
request membership without me being actively involved. Could the person
recommending the group send a link?
The groups home page, showing the email commands, the join button, and other information about the group is available to non-members. The group's home page is probably the most useful link to provide when recommending the group - just as I've done.
Related to this is that I haven't seen groups.io groups come up in
google searches, yet yahoo groups are very findable by their subject
matter.
They can be found in Google and other web searches. But it is true that groups.io is not yet as well known as Yahoo Groups, and there are far fewer groups here as yet. You can help your group's search ranking along by posting links to your group in many public places on the web (where appropriate, I'm not suggesting comment-spamming or other abusive techniques).
-- Shal
Shal Farley