In a blog post, the US model reflected on "the crushing weight of regret for the things I've said in the past".
Teigen published a series of tweets in May apologising to TV personality Courtney Stodden, who accused her of online bullying.
In her latest blog post, Teigen said she was privately reaching out to people she'd insulted in the past, though she did not say who.
"There is simply no excuse for my past horrible tweets," wrote Teigen, who is married to singer John Legend. "I was a troll, full stop. And I am so sorry."
"I took to Twitter to try to gain attention and show off what I at the time believed was a crude, clever, harmless quip. I thought it made me cool and relatable if I poked fun at celebrities," she continued.
"In reality, I was insecure, immature and in a world where I thought I needed to impress strangers to be accepted," Teigen added.