Rocket Internet (RKET.DE), the global e-commerce investor, expects to launch at least another 10 start-ups in 2015 and said it would work more closely with Facebook (FB.O) on advertising.

Rocket Internet, whose shares have had a bumpy ride since listing last month, said its 12 most successful companies saw average growth in gross merchandise volume -- a measure of sales made through online marketplaces -- of 104 percent in the six months to June 30.

It also announced a global agreement with Facebook, which will involve the U.S. company helping Rocket with advertising strategy and automation of ads and giving it access to tests of new advertising features.

Rocket Internet shares, which have rebounded to above the offer price of 42.50 euros after positive broker notes in recent days, were up 0.2 percent at 47.92 euros at 0940 GMT.

Investors who bought shares in Europe's largest tech listing since 2000 were hoping to ride a wave of euphoria which culminated in Alibaba's (BABA.N) bumper New York flotation. However, the shares came under pressure over concerns about how long it might take the Rocket start-ups to turn a profit.

Among Rocket's top performers were Russian fashion site Lamoda and Indian online store Jabong, which saw first-half revenue grow 112 percent and 187 percent respectively.

Founded in 2007 by brothers Oliver, Alexander and Marc Samwer, Rocket has set up dozens of e-commerce and online marketplaces for everything from taxis to meal deliveries, aiming to replicate the success of Amazon (AMZN.O) and

Alibaba in new markets like Africa, Latin America and Russia.

Chief Executive Oliver Samwer said the new businesses were on track towards profitability, reiterating his view that e-commerce start-ups take six to nine years to break even.

"Our opportunity is huge and our journey has just begun," he told a media conference call.

Overall, the 12 top companies, while still-loss-making, saw an average rise of 12 percentage points in the margin on their average earnings before interest, taxation, depreciation and amortisation (EBITDA) compared with the figure for 2013.

Rocket expects to launch another three companies in 2014, bringing the total for the year to 10, and then start at least another 10 start-ups in 2015.