SELECT DISTINCT(a1.actor)
FROM actions a1
JOIN actions a2 ON a1.ip = a2.ip
WHERE a2.actor = 143
AND a2.ip != '0.0.0.0'
AND a2.ip != ''
AND a2.actor != a1.actor
AND a1.actor != 0

+----+-------------+-------+-------+------------------+---------+---------+------------------+------+--------------------------+
| id | select_type | table | type  | possible_keys    | key     | key_len | ref              | rows | Extra                    |
+----+-------------+-------+-------+------------------+---------+---------+------------------+------+--------------------------+
|  1 | SIMPLE      | a2    | range | actor,ip,actorIp | actorIp | 66      | NULL             | 3800 | Using where; Using index |
|  1 | SIMPLE      | a1    | ref   | ip               | ip      | 62      | formabilio.a2.ip |   11 | Using where              |
+----+-------------+-------+-------+------------------+---------+---------+------------------+------+--------------------------+

SELECT DISTINCT(a1.actor)
FROM actions a1
INNER JOIN actions a2
ON a1.ip = a2.ip AND
   a1.actor <> a2.actor
WHERE a2.actor = 143
AND a2.ip <> '0.0.0.0'
AND a2.ip <> ''
AND a1.actor <> 0

CREATE INDEX _actions_ip ON actions( ip );
CREATE INDEX _actions_actor ON actions( actor );