Avenir belong to the 3rd group.
Avenir is conjugated the same way that verbs that end in : -enir
Avenir is conjugated with auxiliary avoir.
Avenir is a defective verb. It can not be conjugated in all possible forms.
Avenir verb is direct transitive, intransitive.
Conjugation rules 6d115e
Avenir is a defective verb. This verb only exists in infinitive, in present participle and present gerondive.
Here are several examples of defectives verbs: paître.
Finally, the interrogative form does not exist in subjunctive and imperative.