I don’t think you can do it Jessica. I have never tried. You can follow people I think, although in 8 years of posting here I have never done that. I check YLF often enough that I can see where someone has replied to a question or comment in a thread. If you really want a particular person you are able to send them a personal message. They will only see it next time they go on the forum I think, but maybe they get an email as well? I forget because I haven’t been sent personal messages on the forum for a while. The only way you can’t send a personal message is if the person has blocked you, which people do occasionally. If you block someone then when logged in you don’t see any threads they have started.
If I have any of this incorrect then hopefully someone will let me know!