People get bombarded with loads of emails everyday, so when you don’t get a response from an employer, chances are he/she isn’t ignoring you, your email is just on the bottom of the list. The responsibility lies on the sender to nag (politely) until a follow-up has been given. Here are a couple of ways to nag politely.

• Be overly polite and humble. Never take your feelings out in an email, don’t get mad, rather show that you are friendly and understanding of the lack of response.
• Persistent doesn’t mean every day. Don’t bombard the contact with emails daily. Stagger them out weekly.
• Ask if you should stop reaching out. After a while, if no response is forthcoming directly ask if you should stop trying.
• Stand out in a good way. Try to relate or show interest in the contact (Facebook stalk them for hints).
• Change it up. Try sending the email at different times of the day, in hopes of catching the person in a different mood or when they are not busy. 

[ Source : Mashable ]