1
Whom do you think will win the match?
Who do you think will win the match?
Use who for the person who does the action. Here, that person will win the match. The words ‘do you think’ do not change this.
2
That is the man whom we think stole the money.
That is the man who we think stole the money.
If the person the relative pronoun refers to (‘the man’) did the action in the relative clause (‘stole the money’), use who, not whom. The words ‘we think’ do not change this.
Use whom when the person receives the action, especially in formal writing: ‘That is the man whom we think the police arrested.’ Here, the police did the action, and ‘the man’ received it: he was arrested. In everyday English, who is also common in this sentence.
See WHO