[Anzipane!]

You need to format the string. (The IP is a string so you should use "%s" identifier)
Example:

pawn Код:

new plrIP[16], string[32];
    GetPlayerIp(playerid, plrIP, sizeof(plrIP));
    format(string, sizeof(string), "IP: %s", plrIP);
    SendClientMessageToAll(COLOR, string);

EDIT: oh, JaTochNietDan replied faster than me.