HAMBURG, June 18 (Reuters) - Privately held German firm Otto, the world's biggest mail-order group, said sales rose slightly in its first quarter even as the global economy slumped, adding it will invest heavily to expand.

Bikinis at Otto

"We will be successful in the current fiscal year as well despite the economic crisis," chief executive Hans-Otto Schrader told reporters on Thursday 18 June after posting full-year results.

Schrader gave no detail for sales in the March-to-May quarter, but said turnover in the year to February edged up half a percent to 10.1 billion euros ($14.1 billion). Sales rose 1.9 percent adjusted for currency swings. Its full-year profit advanced 15.9 percent to 321 million euros.

The world's second-biggest online retailer after Amazon.com Inc (AMZN.O) competes against companies including Neckermann and involvent group Arcandor's (AROG.DE) Primondo/Quelle business.

Otto, whose brands include Baur, Bonprix and Crate and Barrel, has said it might buy parts of Primondo. [ID:nL0691652]

It has been divesting assets such as a 34 percent stake in French financial services group Cofidis to help cut debt by 70 percent, or more than 6 billion euros.

Its family owners have also injected fresh capital into the group to strengthen its finances. (Reporting by Jan Schwartz; Writing by Michael Shields; Editing by Dan Lalor) ($1 = 0.7165 euro)