The Japanese driver raced for Sauber since the start of 2010 but was replaced by Nico Hulkenberg for next season.
Kobayashi set up a donation fund, for which he thanked supporters, but conceded his efforts came too late in the year.
"Because of your big support, it gave huge influences to some Japanese companies and I started receiving good support from them. I was in the position to bring a budget of 8 million Euros at least. If you could imagine the time I had, it was [an] overwhelming reaction and it shows there still is a great potential from Japanese companies," he posted on his official website.
Kobayashi confirmed F1 is not on the agenda in 2013, but is hoping for a return in 2014.
"Unfortunately, the time was still short and I am not able to secure the seat with [a] competitive F1 team for 2013. I have to admit that it is very sad and [I] feel sorry for fans and Japanese companies who supported me. But I am still confident to make it happen in 2014."
"I would like to stop the donation for now and while I will save all the money for 2014, I start to look what is the best option for 2013 and also 2014. My main priority is to secure the competitive F1 seat in 2014."
"I have no interests to race any other categories," he added.
Kobayashi has started 60 races, with a best finish of third in the Japanese Grand Prix this season.