* Germany's Helpling buys Britain's Hassle.com
* Move comes as U.S. pioneer Homejoy in retreat
* Signs volatile "Uber for home help" market maturing
By Eric Auchard
FRANKFURT, July 3 (Reuters) - Booking household cleaning services online, one of the more cluttered areas of start-up investment recently, is undergoing a clear-out of its own as two European market leaders merge, while the U.S. pioneer in the field appears to be in retreat.
Germany's Helpling said on Friday it had acquired Britain's Hassle.com to boost its early international lead in the market for busy urban professionals who increasingly go online to book service providers such as home cleaners.
Financial terms were not disclosed.
The two firms aim to do for home cleaning what Airbnb and Uber have respectively done for room-sharing and ride-sharing -- using Web or mobile phone bookings and user reviews to upend an established market.
But whereas Airbnb and Uber quickly built the scale to dominate their markets, online cleaning services is a more open field, with U.S. pioneer Homejoy apparently in retreat after a rapid expansion in the United States, Canada and then Europe.
The Homejoy site no longer accepts bookings in Canada, France or Germany, though it does schedule cleaning appointments in London, its last European outpost.
That means the Helpling-Hassle.com combination could be one of the first examples of European start-ups outpacing U.S. counterparts, though there may be more deals to come in the sector. While firms such as Handy and Porch are still expanding, dozens of other start-ups appear ripe for consolidation.
Together, Helpling and Hassle.com count 100,000 active customers on a monthly basis in 200 cities in 14 countries, Helpling co-founder Benedikt Franke said in an interview.
But while success depends on gaining scale faster than rivals, adoption of online booking of household services faces challenges both in finding nearby qualified cleaners and overcoming users' fears of inviting strangers into their homes.
"This business only works at a local level," said Alex Depledge, one of Hassle.com's three co-founders, who will become chief executive of Helpling's English-speaking markets.
Recent media reports have suggested Homejoy, founded by a sister-brother team in their 20s, has been offering deep discounts on its housecleaner services to draw new clients, while two top-level executives have departed this year.
Homejoy did not respond to requests for comment on these reports. A Homejoy blog post last month suggested it was expanding into general handyman services in select U.S. markets.
Helpling co-founder Franke declined to comment on whether his company had backed out of talks to acquire Homejoy as reported by one Silicon Valley finance publication in May.
Founded early last year, Helpling built up a warchest of 56.5 million euros ($62.7 million) to become the sector's best-funded start-up, backed by top European Web investors including Rocket Internet, Lakestar and Mangrove Capital.
The Berlin-based firm has expanded to six countries in Europe and erected beachheads in the Middle East, Latin America and Asia, aided by the acquisition of a Singapore rival.
Hassle.com, the first European company to focus on booking household cleaners online, is the top name in Britain and Ireland and is also active in France. It was backed by another top European venture capitalist, Accel Partners, which led a $6 million investment round in the London-based company.
$1 = 0.9010 euros Editing by Mark Potter