It sounds like this book!
***
Border War (A book in the Invasion USA series) (2006)
A novel by
J A Johnstone and William W Johnstone
Not since the days of the infamous Pancho Villa, has a
foreign force raided American soil for plunder.
And when a busload of American schoolgirls is hijacked
and taken across the border into Mexico, the repercussions
prove to be deadly.
The gang of kidnappers is led by the ruthless crime lord
Alphonso Guerrerro, whose daughter is on that bus.
His ex-wife took his daughter back to the States, but
Alphonso wants her back - it’s a matter of pride - and
will stop at nothing to get her.
Now he’s got a devil’s bounty of young women to be used
as hostages, or sold into the horrors of white slavery
in South America if his demands are not met.
But, Vietnam vet Tom Brannon has something to say about
this.
His niece is on that school bus, so he’s recruiting a
battle-tough squad of ex-soldiers made up from the
families of the kidnapped girls.
They’re going to rescue the girls and destroy Guerrerro
and his gang of border thugs once and for all.
"Hunted" comes to mind. Good stuff.