(TMZ) - Lamar Odom has vanished and everyone in his life fears the worst -- that he's off somewhere on a drug binge... TMZ has learned.

Sources connected to the NBA star tell TMZ people on Lamar's side, and on the Kardashian side have not been able to find Lamar or contact him for nearly 72 hours -- and main concern is he's hiding out while doing crack cocaine.

As TMZ first reported ... Khloe Kardashian threw him out of the house Wednesday after attempting an intervention which Lamar squarely rejected.

Lamar's been battling addiction for at least 2 years -- and even reluctantly agreed to go to rehab in San Diego a year ago ... although he bailed after 3 weeks.

Sources tell TMZ Lamar has gone off the hinges since basketball season ended and he became a free agent.

His drug addiction is the core reason why his marriage to Khloe has fallen apart.

Short story ... everyone's worried.