* Sees German ad market up just over 2 percent in 2016
* Sees 2016 German ad revenue growth slightly below market
* Sees 2018 sales at 4.5 bln euros vs 4.2 bln previously
* Shares drop 4.7 pct underperforming media index (Rewrites to focus on ads outlook, adds CEO comment)
By Harro Ten Wolde
FRANKFURT, Oct 13 (Reuters) - German broadcaster ProSiebenSat.1 expects to lose ground to rivals in the German TV advertising market this year but raised forecasts for overall sales as its online businesses got a boost from TV promotions.
"The growth of ProSiebenSat.1's net TV advertising revenues is expected to be slightly lower than market growth in 2016," the company said at its annual capital markets day, suggesting its main rival RTL Group may gain market share.
Until this year, ProSieben has been steadily increasing its share of German TV ads, reaching 44.4 percent at the end of 2015 ahead of RTL on 33.5 percent, according to a ProSieben presentation based on Nielsen data.
ProSieben Chief Executive Thomas Ebeling told analysts October ad bookings were weaker due to lower spending by its four top advertisers, which include Volkswagen and Microsoft, but said bookings for the coming months were above last year's level for now.
ProSieben's conservative outlook for TV advertising overshadowed upgrades to overall sales forecasts for both 2016 and 2018, which it said were down to its strategy of promoting online portals on television channels paying off very well.
In 2015, German language broadcasting accounted for two-thirds of its 3.26 billion euros revenue with digital services contributing 26 percent and the rest from content production.
The company's shares were down 4.7 percent by 1418 GMT, the worst performers in the STOXX Europe 600 Media index, which was 1.4 percent lower.
ProSieben, which broadcasts hit shows such as "Germany's Next Top Model" hosted by Heidi Klum and diet programme "The Biggest Loser", also owns comparison website Verivox, a cluster of travel websites including Ueberflieger.de, a video on demand platform and a TV production company.
The company gave a glimpse of its third-quarter results due on Nov. 3, saying sales were expected to rise about 15 percent and recurring earnings before interest, tax, depreciation and amortisation (EBITDA) should be up more than 10 percent.
ProSieben, which entered the German blue chip index this year, said it now expected 2016 sales to rise by at least 15 percent, up from a previous forecast of at least 10 percent.
RTL Group, which is controlled by Bertelsmann, has pencilled in 2016 revenue growth of 2.5 percent to 5 percent, mainly driven by its digital and German broadcasting businesses.
ProSieben raised its 2018 sales forecast to 4.5 billion euros from 4.2 billion euros and bumped up its EBITDA target for that year to 1.15 billion from 1.1 billion.
CEO Ebeling said he expected the company to draw about 1.4 billion euros of advertising money away from print media by launching TV channels targeted at specific consumers in fashion, health and food markets, in tandem with online platforms.
"TV can drive revenues of these platforms. Platforms can achieve relevance for our advertisers," Ebeling said.
ProSieben, for example, saw a 50 percent rise in average daily revenues at its online erotic shop Amorelie after its first television ad campaign, and then another 120 percent sales jump following a second campaign.
$1 = 0.8928 euros Editing by David Clarke