Keltec's website states that +p can be used but not for continuous use.
I know Im late to this, but I recently tried sum Winchester Ranger Nato rounds in my Kel-Tec PF9 and I believe those are +P and I havent had an issue. I only ran maybe 2 mags thru it to be safe. Ive heard that you shouldnt continuously feed most pistols with +P ammo because it will wear them down, so I havent done it that much.
"Just like the P-11, the PF-9 will accept +P ammunition, however, not with continuous use." This is on Kel Tec's website in the Pf9's description. Personally, I am not comfortable with using +p ammo in my PF9 because although I love it, it IS cheaply built.
I have a PF-9 and I use standard pressure either 115gr or 147gr JHPs and I carry a spare mag with NATO spec 124gr JSP.
P.S. My first post!!
I have scored a few boxes of a Mag Tech 92.6 grain solid copper JHP's that the P-11 seems to like, and these are standard pressure loads that are speedy!