I don't know how other people add massage places to LINE, but I can tell you what I did. I would click on links to different massage places that would be provided in messages on this site, but also on ShamelessMack2. Usually the link will take you to a website, Facebook page, or X account where they will have their link to LINE posted. Click on the LINE link and their QR code will appear. Open your LINE account on your phone, then 'add friends' and scan their QR code. I didn't really need to do anything beyond that to get on the daily mailing list...it just happened automatically. Once I added them as a friend, I started receiving updates daily...that is until this week. There is usually some text as well, but all in Thai.
As for a list of massage places, I don't think such a thing exists. From what I have been able to discern from this forum and at ShamelessMack2, massage places come and go, change ownership, and change locations. This seems to be a normal occurrence in Thailand. Other members may know of a list or a better way to utilize LINE. I am fairly new to the scene in Thailand. Been several times, but always traveling with straight friends and never had the opportunity to venture out on my own until August 2024. Planning a return solo trip in October.