How do you decide on a surgeon if he only has very few reviews online? An there old reviews?

I agree with other answers that 'negative' reviews mean more than the number of 'positive' reviews. Always consult with a board certified Plastic Surgeon before deciding on a treatment. This post is not intended to be medical advice and is for informational purposes only.

Online reviews are just one of the many sources of information available to you. Lots of negative reviews may be a "red flag"; the presence of just a few reviews may not be meaningful. I would suggest starting with the American Society of Plastic Surgery and/or the Aesthetic Society of Plastic Surgery to obtain a list of well experienced board-certified plastic surgeons.
Then, I would suggest you visit a few surgeons whose practices concentrate on aesthetic surgery. Ask to see lots of EXAMPLES of their work and preferably speak/see patients who have had similar procedures done.
Be very careful with your decision-making. You will find, while doing your due diligence, that there are many different “specialties” who will offer their services to you; again, I strongly recommend you concentrate on surgeons certified by the American Board of Plastic Surgery. I hope this helps.