Backing for independence among young people able to vote for the first time in September has increased to 29 per cent, up from 23 per cent this time last year, according to research by Edinburgh University.
The proportion backing No fell from 58 per cent to 52, with don't knows unchanged on 19 per cent.
The findings came as the referendum battle dominated First Minister's Questions yesterday, with Alex Salmond coming under pressure to spell out the costs behind promises to improve welfare in an independent Scotland.
The university survey questioned more than 1000 under-18s. Stripping out undecideds, 36 per cent said they would vote Yes, up from 28 per cent last year - and 64 per cent said No, down from 72 per cent.
The economy and how young people felt about an independent Scotland's prospects emerged as the biggest single factor in how they planned to vote.
Some 72 per cent of those eligible to vote said they were "very" or "rather likely" to vote in the referendum, a big increase on a year ago.
Dr Jan Eichhorn, who coordinated the study, said: "Apart from the increased support for Yes amongst voters under 18, the most important insight from our survey is about the high level of engagement young people show. Voting turnout can be expected to be much higher than in normal elections and very close to adult levels."
A spokesman for Yes Scotland said: "It is encouraging so many young people are engaging in the debate about Scotland's future, and that support for a Yes vote is increasing."
Better Together youth representative Iona MacDonald, 16, said: "It's encouraging the vast majority of young Scots believe the brightest future for Scotland is to remain in the UK."
In a separate survey of 68 financial advisers in Scotland, three-quarters said they would vote No. The poll, conducted for financial software company Intelliflo, uncovered concerns about possible administrative changes if Scotland left the UK.
At Holyrood, the First Minister faced fresh calls to spell out the cost of promises to increase benefits, pensions and childcare if Scotland becomes independent.
Scottish Labour leader Johann Lamont accused Mr Salmond of trying to "dupe" voters with pledges he could not afford to deliver. She said the Yes campaign was based on "fingers crossed in the hope that the people of Scotland will be daft enough to believe a word the First Minister says".
Scots Tory leader Ruth Davidson accused the First Minister of responding to think-tank reports warning an independent Scotland would start life deeper in the red than the UK with "shrill assertions and bully-boy bluster".
She highlighted comments by his economic adviser Professor Andrew Hughes Hallet, who this week produced estimates for oil revenues lower than the Scottish Government's own figures.
Mr Salmond dismissed the attacks, telling Ms Lamont his Government had produced a clear "framework" for establishing an independent Scotland.
Meanwhile, the cross-party Yes Scotland campaign launched an initiative to bring business people and trade unionists together to discuss labour market reforms in an independent Scotland.
The move follows the publication this week of the Wood Report on skills and plans to change the welfare system, including a steep rise in the minimum wage.