BERLIN, Germany — Rocket Internet SE shares fell the most in more than four months after a writedown of the value of online retailer Global Fashion Group contributed to a a first-half loss of €617 million ($690 million) at the startup factory.

Shares of Rocket dropped 12 percent to €16.61 at 9:24 a.m. in Frankfurt, on track for the biggest decline since April 27. Global Fashion Group had a negative impact of 383 million euros on earnings, Rocket said in a statement late Thursday.

The impairments at Global Fashion Group and other investments the company did not detail validate the concerns of some investors over how Rocket Internet values its assets. The profit warning shows the financial impact of the company’s “overconfident” valuation methodology for its holdings, Jefferies said in note to clients.

“We are satisfied with the operating development,” Rocket Internet chief financial officer Peter Kimpel said in conference call with journalists. He said nothing the company reported is outside market expectations.

Results were also affected by special items such as impairments, fair-value adjustments and to a "lesser extent" positive special items, the company said without elaborating.

Rocket, which holds dozens of startups in areas including food delivery, furniture and fashion, was founded by German entrepreneur Oliver Samwer and his brothers and taken public in 2014. The company has seen its shares tumble about 41 percent this year as some of its holdings have faltered, while some analysts have questioned Rocket's ability to steer startups operating in unproven markets to profitability. The company's market value on Friday is now about €2.8 billion.

The Berlin-based builder of e-commerce startups in July contributed €68 million to a €330 million funding round for Global Fashion Group, completing a deal first announced in April. The financing valued the online fashion retailer at €1 billion, less than half what it was worth last year. Rocket holds about 20 percent in Global Fashion Group, it said in July.

Sales fell 59 percent to €29 million in the first half as a result of the deconsolidation of some subsidiaries. Rocket Internet said it will report full results Sept. 22.

By Stefan Nicola, Aaron Ricadela, Kim Robert McLaughlin and Claudia Rach; editors: Anthony Palazzo and Kim Robert McLaughlin.