UPDATE 1-Fashion conscious Boohoo online sales bloom, lifting shares

(Adds shares, reaction)

LONDON, Sept 5 (Reuters) - Britain's Boohoo raised its full-year revenue forecast on Thursday on strong demand from its young customers for brands like PrettyLittleThing and Nasty Gal, sending the online fashion firm's shares to an all-time high.

Shares in Boohoo, founded 14 years ago in Manchester, northern England, rose as much as 17% to an all-time high of 285.3 pence, as it said it expected its full-year revenue to rise between 33% and 38%, ahead of its previous 25% to 30% guidance, which would deliver a corresponding rise in earnings.

Online retailers like Boohoo are growing fast, often at the expense of traditional shopping outlets such as Marks and Spencer, whose share price fall has seen the 135-year-old retailer evicted from the blue-chip FTSE 100 index on Wednesday.

Boohoo had defied weak consumer confidence to deliver "another stellar performance over a warm summer", analysts at Jefferies said, forecasting a 3-4% rise in consensus for sales and core earnings in the year to February 2020.

Boohoo, which reports first-half results on Sept.25, said it expected margins to remain at around 10%, reflecting investments in the three brands - MissPap, Karen Millen and Coast - it acquired in the first half. (Reporting by Paul Sandle, editing by James Davey and Alexander Smith)