I got a utility with the help of one of my colleague to find where is a custom web part used in SharePoint page?
Download the utility from the below link.
1. Open CMD
2. Navigate the path where you have placed the utility
3. Run Utilityname.exe sitecollectionURL nameofthewebpart
GetWP.exe http://test.contoso.com view
Where GetWP.exe is the utility name, http://test.contoso.com is the site collection URL and View is the name of the webpart. Full name is not necessary for webpart, you can use any sub string of the name. eg. listviewrollup = view
Hope it helps someone.