They don't command them, but they call them in like you call the police.
Fun fact: From time to time, a pilot forgets to change frequency when entering a new area. This means the plane looks like it is not communicating. This is the most common reason why jets are sent to intercept an airliner. Of course, I would pay to see a recording of the pilots as they see the jet in front of them and realize they messed up.
I think switching to a frequency that a different region uses could be dangerous, since then the airplanes near do border would receive the signal but the airport wouldn't. This could lead to misscommunications.
PPS: They do try the emergency frequency, routing a message through the previous area controller as well as anything else they can think of first. I left it out for brevity. Of course, fighter jets are not the first choice.