So how soon and how often is it OK to follow up? After the interview, they told me I will hear from them in 2 week (which was Thursday 27 March).

Dear Mr. Salman, Thanks for your invitation,

It depends on the company profile, how many time they take. Some of the companies take more time and several interviews for shortlisting. However if you feel some positive response during the interview, and the company is reputed with the huge activities then it is better to wait for one more week, after that you may ask for any development regarding that position. Insha Allah you will get a better and positive response…… All the BEST…

I would definately advise you to follow up within24 hours saying how much you enjoyed the interview and also include whether or not you would take up the position if offered it. 

If they have informed you it would be a two week window before you found out the outcome i would include that in my email by saying I look forward to hearing from you in two weeks.

If you haven't heard by then drop them an email or call them.

Hope this helps in the future.

Jim

After appearing for an interivew, just write a thank you letter for your consideration.  Show your experience in interivew how it went.  Just wait for one week and just follow up with an email and ask about the status.

Dear Mr. Rizwan, Many thanks for suggestion. Alhamdulillah my interveiw went good & they showed lot of positive intent. The interviewer spends more time talking in detail about the position, organization and begins to told me in detail all the advantages of working for the company.

Dear Mr. Assad,Thanks alot for guidance.