AA usually means African American. It can also mean "acting/appearing", as in "I am a straight a/a gay male".
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.
Pay to play
Alcoholics Anonymous of America. Unless he works for the Automobile Club of America, also known as AAA.