Where do you find volunteers to help with open source projects? Such as:

• https://www.codeshelter.co
• https://hacktoberfest.com
• https://summerofcode.withgoogle.com

For example, with KeenWrite, I'm looking for help help with a specific feature that could be applicable to a wide audience (i.e., academia and technical writers). The lion's share of the effort for cross-references would be an extension or change to the flexmark-java library: parsing a de facto standard cross-reference syntax, rather than direct changes to my text editor.