No. 1 daily deals website Groupon Inc is turning to executives from Citydeal -- the European business it bought last year -- to help boost slowing growth in its domestic business, ahead of a planned public listing.

The company appointed Christopher Muhr as its sales chief, taking over from Darren Schwartz, a source familiar with the matter who did not want to be named, said.

Muhr is moving from London where he was managing director of Groupon UK.

The move seems aimed at tapping into the strength of the company's international team as growth in its domestic market starts to mature.

In June, Groupon filed to raise up to $750 million in an IPO, expected to be one of the most high-profile new listings of 2011.

Groupon's valuation has dropped 20 percent to $16 billion in the latest private auction of shares, according to brokerage Wedbush Securities.

Wedbush partly blamed that on the market slump, but also highlighted slowing sales growth as a concern.

Groupon's recently amended S-1, indicating rapidly decelerating Q2 growth, did little to help drive investor interest in the shares, Wedbush wrote in a note to investors on Tuesday.

Second-quarter revenue at the company, which offers group-buying deals on everything from spa treatments to flying lessons, was up 36 percent, down from the 63 percent increase it posted in the first quarter.

Groupon ended the second quarter with just over 115 million subscribers -- an increase of 32.6 million subscribers -- which Wedbush called disappointing. Most of the slowdown in growth was in the U.S., Groupon's most mature market.

Revenue per subscriber fell 12 percent to $8.57 in North America, according to Yipit, which tracks the daily deal industry.

Joining Muhr at the company's Chicago headquarters are members of the international management team, including fellow Citydeal co-founders Rajen Ruparell, Emanuel Stehle and Jens Hutzschenreuter, the source said.

The changes were communicated to Groupon employees last week, the source said.

When contacted, a Groupon spokeswoman did not immediately confirm the appointments.

Germany's Citydeal, which Groupon bought last year, was used by the company to kick-start its international operations.

(Reporting by Nivedita Bhattacharjee in Bangalore; Additional reporting by Alistair Barr in San Francisco; Editing by Anthony Kurian, Sriraj Kalluvila)