We found their dead horses on the road.
After being ambushed we followed their trail back to a goblin cave. We wiped out everything on the east side of the cave, but the west side remains. We scouted the west side and trapped the bridge separating the two sides, All we have left to do is loot the explored rooms and bodies and then clear the west side.

Rescued Sildar
Gundren has been taken to Cragmaw Castle