@Eugy Yue, "mi piaci" literally is "i like you/我喜欢你". Both english and chinese most of time have a "love" or "sexual" meaning, and so it is in italian. If i say to a boy "mi piaci" in italian seems like i really like him, it's more than a friendship feeling. Sometimes you can use it with a "friend meaning" if you talk to a third person.

If i say to you "lui mi piace" (= i like him) it's something not really clear: i can both mean that i like him as a person (he is funny, intelligent, nice etc.) or that i like his character as like his body, and probably i would like to have some relationship (including love and/or sex) with him. Thus in this situation (with a third person) we prefer to say "lui/lei è troppo forte" ( = he/she is really great), than "mi piace".

As before, between friend is better to say "ti voglio bene" and this for sure express some affection to a person, a kind of love for sure, but not the love we feel for our partner.

So "mi piaci" usually is used with this love or sex meaning. 

Hope i've been clear :)

@Silvia, sì, ho capito bene adesso. Grazie mille per avermi la tua chiarificazione!