What the others said. I believe the laws have changed somewhat, but at one time, a stop-and-frisk that turned up a baggie of contraband would not allow for a good bust, because a soft baggy with leafy matter could not reasonably be mistaken for a weapon in a pocket. On the other hand, one of the things I learned in academy was to get over my shyness about reaching into the naughty bit zone. You got to get right in there, stir things up. Yeah, nobody likes it; giving or receiving. Well some might, but I don't want to know about that.
I had an instructor I will always remember, who challenged the class to frisk him, one by one. We all had a go. He was well-armed, and we found some of the weapons. Missed the razor blade in the brim of his baseball cap and the six-foot motorcycle chain in his underwear at the crotch. The noise that made when he whipped it out and slammed it on the desk and said "That was your head I just caved in" was something I will always remember.
However, I can tell you stories (as all cops can) why we took the rear seats out of our cruisers after each shift and check the floorboards with a flashlight. Scary the things that are found on the floorboards, which were obviously dumped by people being transported who were supposedly frisked for weapons and found to be clean. Yikes.