I would like to use an autoresponder for an email to go out as soon as a new subscriber is added to the list. This subscriber would be added with regular csv file uploads from a list of purchasers. I tried this but the autoresponder didn't go out.
Does this function only work for subcribers through the signup form?
Yes, your correct. The Autoresponder will only trigger for subscribers that have signed up via a sign up form or the API. Any subscriber imported via a list and or manually entered will not trigger the Autoresponder.
Please have a look through Does importing subscribers trigger the 'signup' autoresponder emails? FAQ for more information on this.
I hope that helps!