Have you ever received a message from someone you didn't know? 

Have you ever got this message: "Id like to add you to my professional network."

So how do you generate interest with people who you don’t know so they will connect with you.  Here is what I suggest.

Include a question at the end of your message that will give the perspective connection a reason to respond.  Ask them something that only someone in their position would know. People love being helpful, so asking a prospect for their insight or expertise on a certain topic might make them more inclined to respond. Another is how you found their profile.

Things to consider when writing a connection request. 

Be courteous & professional
Be specific. Get right to the point
Personalize it.
Complement them on something.

Here is an Example.
Hi Chris, I came across your profile after seeing your post about “Benefits Of Reading Daily. Interesting stuff…I so enjoy reading your...