"Every day growing and learning. Trying to be better. You get knocked down, you get up," Justin tweeted at the weekend.
"Back on tour tomorrow. Ready to see u all smile. Time to do what I'm supposed to be doing. Performing. #BELIEVEtour."
The star continued with a series of similar-themed tweets, telling fans "I never want to let any of you down".
Justin had been photographed at California's Newport Beach hotel on January 2 enjoying a suspicious-looking cigarette with his best pal, 19-year-old rapper Lil Twist.
According to TMZ, Justin's mate was "happily rolling blunts" for him and his friends.
Security were reportedly present at the evening party, but no issues arose from the photographs being taken.
TMZ's sources close to Justin claim that Lil Twist is a "powerful negative influence" in Justin's life, and that this is not the first time they have smoked together (whatever the substance may be).
The photographer, Chris Guerra, reportedly called a photo agency claiming he had seen Justin smoking marijuana while driving his car. Lil Twist was seen driving the car when he was pulled over by police.
Justin issued a statement saying his "thoughts and prayers are with the family of the victim".
But it was business as usual for Justin, who shed his shirt at a concert on Saturday night for his first appearance since the incident.