More than 94,000 teenage girls give birth in Britain every year, including 9,000 aged under 16, Tony Blair said.
In a written reply in The Commons, Mr Blair said the unit would work towards cutting the rates of teenage parenthood, particularly under-age girls, to approach the European average.
The latest figures show that while 31 out of 1,000 live births in the United Kingdom were to women under 20, the comparable Continental figures were seven in Switzerland, nine in France, eight in Italy and seven in the Netherlands.
Other data showed that 87 per cent of the 41,700 children born to 16 to 19-year-olds in Britain were born outside marriage, compared with 62 per cent in the USA and just 10 per cent in Japan.
The Unit would also be asked to propose better solutions to combat the risk of social exclusion for vulnerable teenage parents and their children. It is hoped that a report on the issue will be available by December.
Mr Blair condemned previous governments for stigmatising teenage mothers, saying that such an attitude ignored the damage that pregnancy did to the education, employment and life chances of young women and girls.
"Now is the time to act and I will be asking the Unit to develop a constructive strategy as a matter of urgency," he said.
A spokeswoman for the International Planned Parenthood Federation said the trend in Britain was particularly worrying.
She said: "At a time when there are diseases like Aids around, it is really quite distressing that young women are not insisting that their partners use contraceptives."
Mr Blair also called on the Unit to investigate the number of 16 to 18 year-olds with no jobs, no training and no educational opportunities. Such youngsters quickly develop into statistics of social exclusion, the Prime Minister said.
"This Government is determined to end all forms of exclusion and recognises that everyone has something to offer," said Mr Blair.
The Unit, which has power to cut across departmental boundaries, has already produced reports on truancy and rough sleeping. Another study is due out in the autumn covering the country's worst housing estates.Reuse content