Interesting research coming out of Uni of Cambridge.  Can bitcoins be tracked? ... used to have issues with tainting the bitcoins but current technology has lead to practical ways to trace stolen bitcoins.  im not sure what this means for you and me, like what happens if somehow stolen bitcoins land in my hands... but interesting nonetheless.

Video: Stolen Bitcoin Tracing - Computerphile; practical way to trace stolen bitcoins

when you lose you coin, dont waste your time unless you know what to do, reach out to a recovery agent or hire someone to help you get it back. there are people out the. check out DIGITRECOVERY.NET and contact them. this is the only agency i have used, cant speak for the others. they charge after the job is done