When the next song ended, everybody applauded once more, and Harry saw Ludo Bagman kiss Professor McGonagall’s hand and make his way back through the crowds, at which point Fred and George accosted him.
There are no more uses of "accost" in the book.
Show samples from other sources
He accosted me with excessive warmth, for he had been drinking much.
Edgar Allan Poe -- The Cask of Amontillado
A few blocks from home, he was accosted by two robbers.