Our son ran away and was involved in property damage to a tractor in the state of Indiana. He was 17 at the time. Are we financially...

I am sorry for the difficulties you are having, and I hope
they work out for the best.  You did not say if you also live in Indiana, or if your son
crossed state lines when he ran away.  You also did not mention if he was convicted of
the damage to the tractor, or if this is a civil lawsuit by the owner of the property. 
Lastly, who informed you that your son is responsible for the damages, the property
owner or the State/Court?

All of these things will affect
whether or not you will be held liable for the financial loss incurred by the tractor
owner.  In general, parents are responsible for damages caused by
their minor children, but this case is complicated enough I would consult an attorney.
Typically a consultation fee is $50 - $100 (you are not hiring them to try the case,
just for the legal advice) and you can get a more complete and definitive legal opinion
than you can here.  Good luck!