How to deal with a lazy postdoc colaborator as a PhD student? I wonder how to politely handle the following situation as a PhD student. Any suggestion will be appreciated. Thanks in advance for any help you could provide.

I was working for almost one year in modelling some results on the work of another PhD student visiting us. He is supposed to be first author.

After a very hard and intensive work I got some positive results and we realized that part of his data was wrongly interpreted or wrong.

That student left time ago and returned to his home country and I sent him the results in order he could prepare a first draft. Aftersome times with no answers I wrote him again asking for the status of the draft but he had stopped because he was close to defend his thesis.

He became a doctor , continued in his lab, and I sent him the results again, as suggested by my supervisors. 

After many times of asking him for a draft along several months he sent a document with many figures and almost no text or explanations. I've been kindly asking him to fill it with some information in order to work on something. However he has done anything for longer than 3 months. I feel he is not interested in publishing it anymore. He is always answering 'I will send you something'but no answers. 

This work has been extending for almost 2 years already. Other co-authors and supervisors are tired of the situation but they seem not to care about. I have talked about this with the coauthors but not evolution has been observed. I am frustrated as it is been delayed so long and It is not my paper but my work. I am really worried.
Sometimes, when the expected first author of a publication abandons it, one of the others steps up to becoming the driving force behind the writing. If you understand the project well enough and care enough about the writing, that person might be you. 

If you want to do this, you first need to talk to your supervisor and have them talk with the other supervisor. If they agree with the plan, then you don't have to wait for the non-writing author any more, but can go ahead with working on the writing yourself. Authorship order might or might not end up changing, but at least you'll be much more likely to end up with a paper.

Alternately, not all papers that are started get completed.  If it is not important enough to you to invest that level of time and effort, this might be one of those for you, and you may need to move on to completing and writing up your next project.