The petition to rescind Tony Blair's knighthood has now surpassed a whopping 600,000 signatures. Unfortunately, as a Change.org petition it has little chance of success. There will be no debate in Parliament, regardless of how many signatures the petition receives. Change.org petitions have garnered millions of signatures in the past, but there is no evidence they have resulted in anything but failure.
If you still want to add your signature to the petition, you can do so here.
There is currently no such petition on the UK government website.