"We haven't got any expectations regarding money. This isn't necessarily a 'highest bidder wins' situation – it's about finding the best ownership model for Givealittle to secure its future growth and to maximise its impact for New Zealanders," Thomas said.
"We're being as open-minded as possible about the future, and it could mean Spark Foundation retains some interest."
Givealittle raised $18.5m in its financial year to June 2018. In its current year, it has raised a record $31.5m so far, including $10.8m for Christchurch shooting victims.
Impact Ventures director Chris Simcock, who is overseeing the sale, noted to the Herald that Givealittle began life as a commercial venture in 2010, backed in part by venture capital outfit Movac. It was a destination where startups could crowdfund money for a bright idea in the manner of Kickstarter or PledgeMe.
Spark bought it in 2012 and re-fashioned it as a charity vehicle.
Simcock said a new owner could return the site more toward its Kickstarter commercial roots but he saw potential for a "social enterprise" angle as well - or a profit-making venture that puts an emphasis on social values.
He is looking to wrap up the bidding process by the end of July.
Givealittle is the second asset that Spark has opened to outside investors this year.
Spark New Zealand is seeking expressions of interest for investment or partnership with its Lightbox streaming video service, which operates separately from the recently-launched Spark Sport.