Dwayne Johnson -- who worked with Williams in the 2013 film "Snitch" -- penned an emotional message on Instagram ... saying, "You’ll be missed, brother."

"A real pleasure to work with you and call you a friend. Strength, mana & love to your family during this very difficult and heartbreaking time. Go rest high."

Ex-NFL receiver Victor Cruz posted a shot with the actor at a previous event -- "Rest easy my brother. One of the most positive human beings I ever met."

Chad 'Ochocinco' Johnson also paid tribute with an old photo of them together ... saying, "R.I.P. @bkbmg".

Tennessee Titans receiver A.J. Brown used a famous quote from "The Wire" to honor the Williams' role as Omar Little ... saying, "'Omar is coming.' Rest in peace."

Even racecar driver Lewis Hamilton paid tribute -- "Sorry to hear the news. My prayers and thoughts go out to his family. Bless your spirit."

The NBA community also showed love -- the New York Knicks posted a photo of the Brooklyn native courtside in MSG ... saying, "Rest in Peace. We send our deepest condolences to the family of Michael K. Williams."

"A true New Yorker and a friend to The Garden and Garden of Dreams."

NBA's Jamal Crawford said, "RIP Michael K. Williams . Prayers to his family."

"Life is short…Tell those you love, you love them. Try to be a good example. Help someone along the way on your own journey.."

As we previously reported, the 54-year-old actor was found dead by a relative in his Brooklyn apartment on Monday in a suspected drug overdose.

Besides his iconic role as Omar in "The Wire," he was in several TV shows and films ... including "12 Years a Slave," "Assassin's Creed" and "The Gambler."