The grief-stricken grandmother of the 22-year-old soldier had a heart attack and died soon after hearing the news.
Senior government ministers have called up his grandfather, CD Patil, to assure him that all efforts were being made to secure his release.
"The home ministers spoke to me personally, and assured me that the government is doing everything it can. We can't ask for more," he told NDTV.
Sepoy Chavan was posted in Mendhar district of Jammu and Kashmir near the LoC with the Rashtriya Rifles when he went missing on Thursday morning.
The Indian Army said he strayed across the LoC while on regular patrol - something that happens frequently to soldiers from both sides in the region.
"All border patrols have a buddy system. I can't believe my brother accidently crossed over. They (army) should ask his buddy what happened?" he said.
"No one can trust them (Pakistan). We are worried they will torture him, and tell him lies that the army doesn't care about him. That could drive him to take his own life," he added.
According to army sources under normal circumstances it would not have been difficult to get Babulal Chavan back - there are established protocols to do so - but these are not normal times.