How can I end harassing behavior from my Plt Sgt (attempted fraternization)? Is there any specific Army regulation or guidance?

First step - direct interaction. You already stated this hasn't worked.
Second step - 1SG/Commander.
Third step - SHARP.

If every step on that list fails you, then go higher. Open door policies allow approach to Battalion and Brigade Commanders and if ALL ELSE fails (command/SHARP) - approach IG.

Ensure you document everything that occurs. Keep a log with date/time stamps and be as descriptive as possible. It also helps if there are witnesses to the behavior. Save all voicemails, emails, and text messages as well. These will turn it from a "he said/she said" to "here's proof this guy is a creeper."

Good luck.

I don't want to being down the wrath of God. I want just enough to happen that it stops and he realizes that this is unacceptable. Just enough so that he can see that this is not a friendship, it is a workplace comradery that does not invite personalization. I'm all for laughing and joking. The day goes faster and it builds cohesion. But never do I forget my place within that structure. They are all my NCOs not my buddies. We shouldn't have to be silent and solemn robots to maintain that respectful boundary.

UPDATE!!

PSG did PCS and is now locked up in Leavenworth for child pornography. It seems is sex addiction (yes that’s what I meant with overly familiar) has no boundaries.

Charge his ass! Write a statement sheet( several copies) give one to your first shirt, then one to your sgtmjr, and for the CO. If that fails take it to JAG. Personally I’d give a copy to all! You need relief from this. Just make sure you have the evidence I.E. voice mails, texts etc.
The more you have the better off you are!

if you have saved all the messages and voice mails, then show them to the sgm. that will not only end it but the e-6 will also end up with a letter of reprimand in his files.

There’s something more going on with the blurring of boundaries and airing all that personal BS. He is vicariously satisfying something by doing that. Watch yourself, it only gets bolder with his internally justified acceptance. He’s go friggin issues. 20 year LE opinion

Definitely take him off the chain to higher levels of command. He doesn't deserve to be a leader if he's doing this kind of thing. And get it done quick sounds like it might get worse for you.

Be careful how you approach. I had an E6 who got way to personal with his personal life and issues to the point he confided with me that he intended to shoot up the company at morning formation. Showed me his Spanish rife and box of ammo. Of course I informed my CO, who had the MP's show up, and he spent a month on a psych ward. Guess what, a month later he was released, and still in charge of me. Long story short, within six months, I went from Spec-4 to E-2 because he kept his word that he would get even with me. Ended up getting an early discharge (under honorable conditions thankfully). Rank is rank, and if you cross him, it may cost you in the end. You may be better off just letting him vent, as long as it isn't hurting your career.

I am a SHARP VA. I’m glad to see so many people pointing you in the direction of your SHARP office. The question I have is whether or not anything he is saying or doing is sexual in nature. If it is you have a couple different reporting options. Also keep in mind that you can go to any SHARP person and make a report so there are a lot of resources out there. I’d be happy to answer any additional questions you have and let you know what your options are

If nothing else has worked, I suggest you get your documentation of who what when and why you have been violated along with the names of who you've contacted in this regard together. Go to your IG or initiate a Congressional Inquiry into why nothing has been done. Pisses people off, so ensure your facts are straight. Good luck. HOOAH!