Hmm. I would suggest (if there is not one already), a discord chat to send teens to meet up at, and agree on RPs. If they are having issues posting a thread to test who is interested. Or their numbers are low. Then throw them all in the same spot, and help them see each other. Unlike a thread, discord chat is 'live' so they would get a responds back right away if another teen is online.
It may also help to make the bluestar/teen area smaller. Right now I see a 'group connections', 'extras', and 'character ads' but that may be good for organization, but probably not that great for a small group of teens as it makes each area look a lot smaller due to less threads in them. That is just my two cents. It may not even be worth that much.
As for the reason to move to PMs. Privacy may be one small issue, but for me personally the larger issue was I disliked having to ask a Mod or Admin to move my thread to the graveyard when I am done (which is fine for a super long rp, but for short rps is wasting someone's time and cluttering up the graveyard), or having to possibly look at the second or third page to find my thread due to other rps having more recent posts. In a PM, my thread is always there, I now can even make a 'folder' for specific people, and there are no other people making threads cluttering up my area. That is my two cents here.
The only issue I have with PMs is when I make a folder or category, and delete a thread. The number of PMs in that category does not seem to decrease. Not sure if its cause the other person still has the PM in their inbox, or what, but I would not think that would be counted in my side of things. (Edit: I should also point out. A PMs let me delete the thread, and not simply move it to a graveyard. Or a least a visual one)
3rd Edit: Also I am not sure why there is a General Area & BlueStar Area. Basically the only reason for an adult to go to the general area is to do a non-sexual RP, and so the adult would know not to do that there with anyone rather teen or adult. And the general forum had to be monitored anyways? And teens wanting to read other non-mature rps probably could just check to see if the thread had a warning at the first post, or if some icon was used. Unless there legal issues with adults possibly seeing sex scenes between teens.
Mmm, in that case, maybe it would make the site more simple to just have 1 General forum (no star areas), and a rule to take any sex scenes to PMs, and then Mods would just have to watch 1 forum area, and PMs. It be less work since that forum and PMs probably had to be watched already anyways. (And a mod would just have to check to see if both users are adults, not read the entire thread/pm. If one is a teenager, then maybe they would have to check the thread or pm for sexual content. Although I guess adult threads need to be check for the age of the characters, but a page search could be used to check for key words, or quickly look through the posts) Just two more of my cents.