TL;DR

"People" is the direct object of "helps" and the subject of "find."

"Find" is a verb.

"Happiness" is the direct object of "find."

No, "find happiness" is not an object complement.

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He helps people find happiness.

Let's assign a role to each word/phrase in the sentence. The key to the answer is that there are two verbs in the sentence: "helps" and "find."

"He" is the subject of the verb "helps."

"Helps" is the verb being completed by the subject "he."

These are very obvious. For the words/phrases below, I will explain why I have assigned them each role.

"People" is the direct object of the verb "helps." A direct object is a noun that is the recipient of the action of a transitive verb, which "to help" is (in this situation). "People" is being helped by "he," so "people" is the direct object. "People" is not the indirect object of the verb because "people" is being directly affected by the action of the verb, whereas an indirect object is affected, but not the primary object of the verb.

For example, look at the sentence "I gave him the book." The direct object is "book" because that is what is being directly given. The indirect object pronoun is "him" because "him" is who is receiving the book (affected by the action of the verb), but is not directly being given.

"People" also plays another role in this sentence. It is the subject of the verb "find." Therefore, "people" is both the direct object of one verb ("helps") and the subject of another ("find").

"Find" is the verb completed by "people."

"Happiness" is the direct object of the verb "find" because "people" is directly "finding" it.

An object complement must be a noun, an adjective, or a pronoun. Therefore, "find happiness" is not an object complement.