MIP And Possession Of Marijuana Charge

My question involves criminal law for the state of: Washington

Went to a concert and snuck both beer and marijuana in. A cop saw one of my friends with a beer and stopped him. They then came over to where another friend and I were sitting and searched our chairs. They then found both marijuana and alcohol and I was charged with both possession of marijuana as well as a MIP. Were they allowed to search me even though they never saw me with any alcohol? Or because I was with him can he search me too?

Definitely the worst concert of my life.

I would call that probable cause.

Not only that, but if you look on the back of your ticket, I am sure that you will see language that states that security can search anyone that enters the venue.

Sorry.