It depends on how bad the elders want it. When my brother moved he didn't tell any of us where. He just wanted to go live his life. I wanted to find him myself because he's my brother and I was concerned. I found out the street from friends and knocked doors until I found him. We started hanging out again. Poor guy was in a really weird place mentally and emotionally and I didn't blame him.
Anyway, the elders found out from my dad, a fellow elder, that I knew where he lived. One confronted me in the auditorium of the KH and wanted me to spill the beans. I told him he should leave the 99 and go find his sheep like I did if he truly cared about him, or was this purely a punitive hunt for him? He got enraged and it got loud and another elder stepped in or it may have come to blows.
I believe they ended up finding out where he worked and essentially served him outside when he went to his car with a summons to attend their judicial hearing. So yeah, they have their ways if they're determined. They aren't technically supposed to hunt people down anymore, but I'm sure it still happens. My brother's experience was 16 years or so ago.