In the personal ads that I have seen, LOS means Lost or Stolen.
Androgynous
For sex :)
Long Term RelationshipLTR in personal ads means long term relationship.
professional
water sports
Bareback, or no condom
OHAC mean in Relationship
In Search Of
friends with benefits.
"short Message service" in other words text. It's not exclusive to personal ads.
PNP in personal ads means party and play.