Yowie Group's shares have plunged by more than 33 per cent, making it Australia's worst-performing stock on Wednesday.

Investors dumped their Yowie stocks after the chocolate maker dramatically slashed its sales growth forecast for the 2018 financial year, from 55 per cent to 17 per cent.

Yowie blamed the sales downgrade on several factors including its problems gaining traction in the US and Canadian markets.

The company revealed in a statement to the ASX that its North American sales (in the first half of the current financial year) fell by 11.7 per cent, compared to last year.

The chocolate maker also expected greater sales from its Canadian retailers, had it not been for product shipment delays.

Another factor it named was the underperformance of Discovery World, a line of children's chocolates, which come with collectable toys.

Time for a new boss

In addition to its sales downgrade, the Perth-based company also announced the sudden resignation of its chief executive Bert Alfonso.

"Notwithstanding the disappointing revenue performance for the half and the reduced full year sales guidance, the Board would like to thank Bert for his efforts," it said.

Mr Alfonso has been replaced as the company's CEO by Mark Schuessler, who was previously the head of Yowie's North American operations.

Yowie made a $US7.3 million ($9.2 million) loss in the last financial year due to weak sales in the United States.

The company was first launched in Australia and New Zealand in 1995 by Cadbury and Kidcorp.

However, a disagreement between Cadbury and the Yowie creators led to production being halted in the early 2000s.

The Yowie Group was able to secure rights to the chocolates in 2012, and was listed on the ASX in the same year.

At 2.35pm (AEDT), Yowie shares were trading at just 14 cents.

This is a far-cry from its price in July 2015, when Yowie stocks were fetching $1.25.