Troubled young people sent more than 200,000 text messages asking for help last year, says youth charity Youthline.

They also made more than 100,000 calls to Youthline's early intervention services and visited its website more than 100,000 times.

The charity said many young people who contacted the service were on the brink of despair.

"There are many alive today who might not have been without the connection with Youthline and there are countless others for whom a conversation with a Youthline person was the point at which their lives started to turn around," said chief executive Stephen Bell.

Tomorrow, Prime Minister John Key is to unveil a plaque at Youthline House in the Auckland suburb of Ponsonby to celebrate Youthline's 40th birthday.

Mr Bell said despite troubling statistics for youth suicide, depression and substance abuse, Youthline believed young New Zealanders could help transform New Zealand into a more civilised, and compassionate country.

He said New Zealand 15- to 19-year-olds had the highest suicide rate in the OECD and a 2004 survey found nearly 29 percent of 16- to 24-year-olds reported a mental health disorder in the previous 12 months.

"These and other statistics, on issues ranging from anxiety disorders to binge drinking to drug use to obesity to youth poverty to exposure to sexual abuse or violence, point to the challenges facing us as a country and a community.

"However, amidst the gloom, there are also sound reasons for optimism.