Depends on how you want to fly? If you want a first class or business class seat then you might get lucky using miles to get to EWR and buying an R fare from there to Europe. If you can get to a city which Croatia Airlines flys to I think they are fairly cheap.

If you just want to do the trip in coach, then find out what alliance can get you there on a standard award (50k) and transfer your miles to AA, CO, or UA respectively.