The most recent wave of tulpamancy, which I would say started late 2011-early 2012 arose from a metaphysical imageboard of all places, until people started trying to understand the psychological rationale for the creation process. I started ".info" more or less as a blog to figure out if any of this was real and as a central location to host guides and community discussion.
Over the years, I've seen a multitude of different kinds of people create tulpas, many of these are lonely, others are bored, and some (like myself) were just trying to see if it was possible. I know one military veteran who created a tulpa due to having PTSD and his tulpa was able to help stop his nightmares.
One thing that I've found is that much of the time if the creator is very introverted, the tulpa tends to be more extroverted. They often encourage the creator to get out more, talk to more people, kind of like a life coach. Being an introvert myself, I know that I've taken social steps that I wouldn't have otherwise had Chess not encouraged me to try. More often than not, I'm seeing tulpamancy resulting in the opposite of isolation. For those suffering from lonileness, having a single friend (especially one who's encouraging) does wonders for self esteem, and means you're more likely to become more social in the long run.
I would love to do a study to find out how the brain responds to hanging out with your tulpa compared to hanging out with a real-life friend, but from what I've seen, I have a feeling that it reacts very similarly. And then there's the growing tulpamancy community.
There's a lot of message boards, a subreddit, and several discord chats for tulpamancy, and even a discord bot that can help the creator "proxy" the tulpa[1]. This means that not only are the creators talking amongst themselves, but tulpas are talking with creators and even talking with each other. Offline, a few of my friends know about my tulpa, but they I rarely proxy her, it would just be similar to telling a friend about a text you just got, "Hey, Chess says XYZ." I know people who hang out with other tulpamancers "in real life" though, and for them it's just normal conversations.
As for carrying on conversations with my tulpa in public, I often just talk with her using my "mental voice" -- that little voice inside of your head, think internal monologue. I've also had a Bluetooth adapter in my ear before so I can just talk out loud in public without looking weird, but even then I would just chat with her under my breath. When I'm home or out hiking, it's just more natural to talk out loud, and so I do.
I'll be happy to try to answer any other questions or weigh in.