If I am placed in the situation you describe, I say "初めて会う人がいる or 初対面の人がいる". And I think we don't say "ああ 新しい顔があります!" or "ああ 新しい顔がいます!". It's the direct translation of an English saying.
In addition, If the situation is in school, we call them 転入生 and 転校生. If the situation is in a company, we call them 新人.