On obtaining references from people who don't know me in person but have cited my work I'll be applying for a few academic positions (both postdoc and permanent positions in Western Europe.) I've done my PhD in pure math (from the US) and subsequent postdocs mainly in use of machine learning in medical imaging and also partly in statistical machine learning (all were in Western Europe.)
I wrote to my PhD advisor regarding the above, who is familiar with my doctoral (pure math) work but isn't familiar with my recent work. While he'll still send the recommendations, he advised me that I should contact people who cited my work and ask them to see if they can write a recommendation.
I don't doubt my advisor's opinion, and I've deep respect for him as a mathematician, but the only thing that I'm asking myself is that if the above strategy will work outside pure math. While I was applying for pure math postdocs back in the day, it did work. But will it work for applied areas like medical imaging or statistical machine learning?
Thank you in advance!
Personally, I'd worry about this strategy for use for a permanent position. A bit less for another postdoc. Your papers speak for themselves without reinforcement by a letter writer except in, perhaps, exceptional cases.
I think the purpose of a letter of recommendation is to go beyond the product you produce and speak about your total fitness for a position. Someone who doesn't know you at all can hardly help you with that.
I'd guess that letters from postdoc PIs, for example, would be better, since you have worked with them.
Someone you know from conference contacts and who has used your work might also be (just) ok, since they can say something about you as a person. Even letters from someone like your old advisor who doesn't know your current work can fill in some blanks about what it would be like to work with you and how diligent you are in various necessary things.
Use the whole application to fill out a whole picture. If you overemphasize one part you will be neglecting other important parts.
If it were just your advisor and, say, two others who don't know you personally and haven't worked with you, then I'd really advise against it. One such letter might be ok if, for example, you've actually communicated with them in the past.