If your friend chose not to complete his deferral, or was summoned for probation violation proceedings and chose not to appear, then he is subject to being re-sentenced for his drug crime. Whether or not you can find a warrant, a warrant would have issued and there is no statute of limitations.

He knows whether or not he completed his sentence. If he did not, he should consult with a criminal defense lawyer about his options for resolving the probation violation and criminal charges.