* Seeks at least 600 mln euros from placement of new shares

* Revenue grew 57% last year to over 1 billion euros

* Profitable in core markets, growing fast in new ones

* B2B commerce platform competes with Shopify, SAP, Salesforce

BERLIN, May 27 (Reuters) - German fashion e-tailer About You said on Thursday it plans to float on the Frankfurt stock exchange, and would invest the proceeds in expanding abroad and developing its business-to-business technology platform.

The Hamburg startup, backed by mail order group Otto and Danish tycoon Anders Holch Povlson, is seeking to raise at least 600 million euros ($731 million) via a private placement of new shares, while existing shareholders would also sell stock.

Sources familiar with the offering said it would value the business at around 3 billion euros.

About You, which competes with Shopify, SAP and Salesforce, said its appeal to younger shoppers and technology platform offered a compelling growth story to investors.

"We are the only company in our sector that has a proven internationalization strategy," co-founder Tarek Mueller told Reuters in an interview.

About You reported 57% revenue growth in the year to February to 1.17 billion euros, and in the last quarter achieved its first positive earnings before interest, taxation, depreciation and amortization (EBITDA) since its launch in 2014.

It cited estimates that Europe's fashion market was worth 400 billion euros, of which 75 billion euros was traded online. It forecasts that online fashion sales will growth at a annual rate of 10%.

Mueller resisted comparisons with Zalando, Europe's top online fashion retailer, saying About You appealed to a younger public that likes to search for outfits before deciding to buy.

"Most of our customers use us to browse. Our competitor is not Zalando – it’s the city centre,” he told Reuters.

Around seven in 10 people in continental Europe live in the suburbs or countryside, he noted. “For them the classic shopping trip today is more attractive on their smartphone," he said.

About You expanded into 13 new markets last year, bringing the number of countries where it is present to 23.

It achieved over half its sales in its core German-speaking markets, where revenue grew by 29% and it made a positive adjusted EBITDA margin of 6%. In the rest of Europe, sales rose 145%, but its EBITDA margin was minus 18%.

Its technology platform, on which more than 60 external shops are already live, reported a 61% increase in revenue last year and positive EBITDA margin of 12%.

About You said it was encouraged by the strong start to its current fiscal year, and forecast revenue growth of 40-50%.

Deutsche Bank, Goldman Sachs, and JPMorgan are acting as joint global coordinators and joint bookrunners on the deal, with Numis Securities, Societe Generale and UBS Investment Bank also acting as joint bookrunners. (Reporting by Douglas Busvine; Editing by Riham Alkousaa and Jan Harvey)