Celeste Rivas' Former Teacher Tells Students She Met D4vd on Social Media

D4vd and Celeste Rivas -- the 15-year-old girl found dead in his car -- are very much on the radar of one of Celeste's former school teachers ... who's now flaunting what he claims to know about their relationship.

The science teacher busted out his phone Thursday in class and told students he had taught Celeste years ago. He showed off a pic of himself with Celeste in front of a poster -- which he still has -- and said she'd "been missing since I taught her."

Remember, Celeste went missing in early 2024, and the teacher claims she first disappeared after meeting singer D4vd (the teacher calls him a rapper) on social media. His version of events is that Celeste allegedly ran away to Hollywood with D4vd, but police tracked her down ... and returned her to her mother.

The teacher says Celeste went missing again in May 2024, and that's the last he heard of her until this week, when police revealed she is the victim whose body was chopped up and left inside D4vd's Tesla.

We spoke to the teacher, who says back when he taught Celeste -- at Lakeland Village School in Lake Elsinore, CA -- she was frequently absent, but he did not know anything about her home life.

While he's now teaching at a different school in Southern California, he clarified he was only sharing this information with students as a "cautionary tale" about the dangers of social media.

The teacher claimed to know another student connected to D4vd ... the kid seen talking to the singer in a Lake Elsinore area parking lot, just a 6-minute walk away from Celeste's family home.

TMZ broke the story ... detectives served a search warrant Wednesday evening at the Hollywood Hills home where D4vd had been living, and law enforcement sources tell us cops scoured the building for traces of blood.