“When I think of all the immense obligations under which I am placed towards you, and at the same time consider how long I have left you without a sign of remembrance, I am perfectly ashamed and miserable, and in despair of ever being forgiven by you! ‘Yes,’ I said to myself with a deep feeling of bitterness, ‘I am an ungrateful fellow; I have forgotten my benefactor, I have forgotten that good master to whom I owe both my talent and my success.’"*
Take your cue from Franz. You don’t have to be as verbose or flowery, but you should consider thanking those who cared both for and about you.
*Letters of Franz Liszt, Volume 1, "From Paris to Rome: Years of
Travel as a Virtuoso" by Franz Liszt; letters collected by La Mara and translated by Constance Bache. Online at http://www.gutenberg.org/cache/epub/3689/pg3689-images.html