The site was hacked earlier last week, but the breach has been repaired, chief executive Yancey Strickler said.
The hackers got some passwords, phone numbers and email addresses, but “no credit card data of any kind was accessed,” he said.
Kickstarter is one the leading online fundraising sites that lets people raise money from donors for projects.
In an email to all members of the site Strickler said: “We’re incredibly sorry that this happened, we set a very high bar for how we serve our community, and this incident is frustrating and upsetting. We have since improved our security procedures and systems in numerous ways.
“As a precaution, we strongly recommend that you create a new password for your Kickstarter account, and other accounts where you use this password.”
He added that the company is “working closely with law enforcement”.
Audere Capital chairman Richard Alvin, backer of a number of schemes on the platform said: “This kind of hack is a disappointment and a setback as alternative funding markets look to replace more traditional sources like banks and venture capital as means of bringing entrepreneurial dreams into reality.”
Kickstarter was founded five years ago and claims to have generated £586m of revenue for more than 56,000 projects from more than 5.6 million people.