To say you miss someone or something, Italian uses mancare — and it works exactly like piacere. The thing or person you miss is the subject; you are the small pronoun:

Mi manca Firenze. — literally Florence is missing to me → I miss Florence.

One thing / person	Several
Mi manca mia madre. — I miss my mum.	Mi mancano i miei amici. — I miss my friends.
Ci manca il mare. — We miss the sea.	Gli mancano le piazze di Firenze. — He misses Florence's squares.

Now the tricky part — talking to the person you miss:

• Mi manchi. — I miss you. (you are missing to me)
• Ti manco? — Do you miss me? (am I missing to you?)
• Mi mancherai / mi mancherete. — I'll miss you / I'll miss you all.
• Past, with essere — agreeing with the person missed: Mi sei mancata tanto, mamma! — I missed you so much, Mum!