What is the best procedure to get rid of thinning skin & dark circles under the eyes?
Several things 'can cause the problems you have. Sometimes just proper skin care can eliminate the darkness. Occasionally, A filler like Juvederm or fat can correct the problem. At other times, surgery is the only answer. See a Plastic Surgeon with experience in all these areas.
Dark Circles Below the Eyes – There is no known treatment for dark circles below the eyes. One can blend the eyelid/cheek junction and can use topical lightening creams including Kojic Acid, Hydroquinone, as well as Retin-A. In general, you cannot completely avoid dark circles under the eyes.