How to find jobs in KSA from Pakistan ?

It is very difficult to get job in KSA when u r sitting in Pakistan. You will have to take azad visa first which is for temporary period and go there to find job. Saudis don't do online recruiting mostly. Half of my family is working there so its a very practical suggestion...
Or if you still wanna try from Pakistan than you can use pakvacancy but i won't suggest u that
http://pakvacancy.com/jobs-employment/saudi-arabia.html

Do you have a residence visa already? If im not wrong your family lives in KSA? well then it's better to come here n start job hunting http://www.expatriates.com/classifieds/saudi/jobs/ but if that's not the case then try what Nabeeha has posted but getting a visa is not that easy anymore. Well it depends on your field too. I'll try to ask some of my job hunter friends and wud let you know if I get any satisfactory answer : )

LinkedIn
Personal Contacts
(Group) Mailing Lists

There is a recruitment agency in Garden Town Lahore which is dealing the same.

There are some websites you can look for them too.. (monstergulf.com, naukrigulf.com, gulftalent.com)

I would suggest you to be careful about few things.

First, you might not get same there when you reach than what was mentioned before in package. (but this is rare)

Secondly and most importantly, there is a big issue in Saudia that expats get the jobs while local Saudis due to lack of education and efficiency are denied, which has resulted in unemployment rate for locals.

And just a month back King Abdullah has announced a rating system, for companies which maintain a balance in jobs for expats and locals, there employees will have job security, while those companies which do not honour the law, their employees will be departed after maybe 3 years (that might hurt you if you're looking for a long term job).