Yahoo7, the Australian subsidiary of search giant Yahoo, has jumped into the group-buying fray and snapped up Aussie deal site Spreets for $40 million, the companies said today.

Spreets is just one of dozens of Australian group-buying companies, which usually feature a deal of the day for members who are offered deals and vouchers at local merchants at discounted prices.

Yahoo7, which is a partnership between Yahoo and Australia’s Channel 7, had clearly been keeping an eye on the company’s booming growth. Founded only a year ago by Dean McEvoy and Justus Hammer, it now claims 500,000 members and broke even in less than 12 months.

The group-buying sector was recently assessed as being worth $100 million annually, making it a tempting target for companies looking to diversify into new and hip revenue stream.

Indeed, investors interested in grabbing a piece of the white-hot social buying market have been throwing money into the sector for months now, as shopping recommendation site ShopSocially announced $1.1 million in first round financing, and Spanish coupon site Groupalia locked down €5 million in its second institutional round of funding.

The industry grabbed headlines earlier this year when well-known deal site Groupon famously snubbed a $6 billion buyout offer from Google. It will reportedly instead plan an IPO that values the company at $9 billion or more.

Today’s deal is part of a larger trend in investments in startup social media sites that focus on spreading the word about shopping deals.

These sites include “friend meet-up” forums like SocialMedia, or companies like Groupon that specialize in finding discount deals on everything from luxury brands to restaurant coupons.

The Yahoo7 joint venture, formed in 2006, acquired Australian travel site Totaltravel.com in 2009.