First of all I would FIRST be very upset with my child. Mine all know better than to just up and leave anywhere before telling an adult.
I believe that it is very easy for something like this to happen. Kids are at recess for 15-20 minutes with a couple adults watching the masses. Their eyes can't be on everyone at every single second. Then they line up..get back into class and it would take a little more time before kids are all in a seat situation before students begin to say "Hey..Johnny is not here!" or for the teacher to notice one of her 25 kids is not there. Then they begin looking around and then contact the office.
Sooo, I can see how easily a 30 minute time period could lapse. If one of my 3 are missing at home it takes me a few minutes to locate.
I would not go to the media..that is just ridiculous. I would work with the teacher and the school administrators. Talk about how maybe they should take roll when they line up to head out to recess or lunch and then take roll again when they line up to come in. Stragglers are always out in the far field or in the restroom taking their sweet time.
At our school the kids get a number identity in their class. This is their number for the whole year. Then when ever they line up they get in number order. You always know there is a gap when the number is missing during number count down and kids get used to who should be in front or behind them. It is another layer for easily paying attention to detail.
Don't go the media route. This type of stuff happens often. We have had kids run away from campus at two of the schools my kids have attended.
Good luck and best wishes.