My Online Boyfriend Disappeared, is it appropriate to send him a letter?..

Its such a long story but ive been mulling over it for a while now. He deleted all his socials and isnt talking to any of our friends in our online community (he did something bad and was embarrassed and ran off, i dont want to go into it.) I was the only person with his phone number but he changed it.. I havent spoken to him in 10 days. His parents know about me but they told him they dont want him speaking to anyone online. (ive never spoken to his parents) Ive felt really heart broken through this whole ordeal and i just dont know if hes coming back or not. In our last phone call he told me we wouldnt be able to talk for a while and he said he appreciated me, but i dont know what to do. He gave me his address a couple months back, would it be weird to send him a letter? I dont want to cross any boundaries Im 18f hes 21m