* Q3 adj. EBIT margin at 13 pct, seen in Q4 at 16-20 pct
* Q3 revenues at $479.6 mln, seen in Q4 at $570-610 mln
* Shares fall 20.5 pct to 30.60 euros at 0814 GMT
* Face recognition sensors for 2 Android OEMs in production
* Works on sensors that scan surroundings for major OEM
* Environmental sensing no longer a strategic focus (Adds analysts, shares, background, secondary listing)
VIENNA, Oct 23 (Reuters) - AMS AG's shares tumbled by nearly a third on Tuesday after the chipmaker's outlook failed to convince investors.
"Guidance for the fourth-quarter 2018 is below consensus and our forecast," Liberum analysts said in a note to clients, adding they were sceptical about AMS meeting its 2019 revenue growth target and operating margin target of 30 percent in 2020.
Shares in AMS dropped by more than 30 percent in early trading and were down 20.5 percent to 30.60 euros at 0814 GMT.
AMS on Monday reported third-quarter earnings above expectations as Apple started mass production of new phones that include its sensors. Apple accounts for around 40 percent of AMS sales, analysts estimate.
Investors in particular are focused on Apple's three new iPhones, which analysts think include AMS's face recognition sensors. AMS hopes that new products launched in the second half of 2018 will boost sales next year.
AMS said its third-quarter adjusted earnings before interest and tax (EBIT) reached $60.2 million or 13 percent of revenue from $40.5 million last year thanks to increasing production volumes for a recently launched global smartphone platform.
AMS does not identify its customers, but this was believed to be a reference to Apple.
The EBIT margin is expected to rise to 16 to 20 percent in the fourth quarter, AMS said.
Revenues in the quarter reached $479.6 million, against 2017's $305.5 million and are expected to rise to $570 to $610 million in the three months through December.
To reduce its dependency on Apple, AMS has been working on selling its sensors to Android customers. This has become more important after the U.S. tech giant agreed a $600 million deal with German rival Dialog Semiconductors this month.
The Swiss-listed company said it has started to produce 3D face recognition sensors for two Android customers, including China's Xiaomi, the world's fourth-biggest smartphone maker.
Credit Suisse analysts think that Huawei's new Mate20 Pro phones also use AMS's sensors for its face recognition feature, which would add the second-biggest smartphone maker to AMS's customers list.
AMS said it was working on sensors that are capable of scanning surroundings in 3D, so-called world-facing 3D sensors, for a major smartphone manufacturer.
It is also in early preparation stages for a secondary listing on the Hong Kong stock exchange, which it anticipates for the second quarter next year. It plans to place up to 10 percent of outstanding shares. (Reporting by Kirsti Knolle; Editing by Adrian Croft and Alexander Smith)