You know it seems to me that he had already figured it out by the old faded poster asking for info on harry put out by the twins in diagon alley and also by hedwig deliverying the old mail that his friends nor the wiz world knew he was in prison, so why the hell didnt he tell hemrione that he had been thrown in prison and he is now out!?!
I have thought Harry has always been a very independent person; As JKR has shown, it can be to a fault. He has been tortured and has some issues he wants o work though before bringing the people he thought had abandoned him back into his life. It will take more than a letter and an old faded poster to set that right.