The man targetted his victims over Kik, a chat app aimed at teenagers and pre-teens, Skype and other social media platforms.
Most of his victims were between 12 and 14 years old, but the youngest was only ten.
Sweden's Göta high court, for the west of Sweden, added an extra year to the sentence given by the district court in Borås, giving the man the maximum possible sentence.
"In more or less everything, we've come to the same conclusions as the district court, but in a few cases we have judged the crimes as more serious," explained Henrik Fernqvist, one of the judges in the case.
"Another difference is that we judged that the man had better knowledge of how young these people were."
"I think it's good, this should reach the limit and be given the maximum punishment," Åsa Askenbäck, the prosecutor in the case, told Swedish Radio.
The man was found guilty of carrying out several hundred cases of abuse over a five-year period, leading some to call it Sweden's biggest ever child sex abuse case in terms of the number of victims.
The man used a fake identity on the forums and used it to convince the girls to carry out sexual acts.
In its judgement, the court described how the man remorselessly exploited the girls' sexual curiosity to make them strip naked, and used threats to publish pictures and films to blackmail them into performing sexual acts on themselves.
He then used threats to publish pictures and films, to force them to endure more abuse.
The man had appealed 60 of the cases ruled on by the district court, claiming that someone else had stolen his user name.