Is it good practice to promote product to contacts using LinkedIn direct message

We have a product which we would like to market using LinkedIn. Now I have a group of contacts(1'st connections) in LinkedIn who are our prospects. But I have never interacted with them. My question is should I send direct messages to them with details of the product or should I engage with them through other groups and promote product using LinkedIn.

Which option is effective?

Direct connections are supposed to be individuals that you personally know. Like in real life, it is perfectly OK to pitch something to a friend, as long as you are in the clear that this is something that he / she is actually interested in.

When you contact them, make sure you include a personal introduction (i.e. "Hi Peter" or "Hi Kate" ) and not just a generic text. Don't just blast it out - there is nothing worse than getting your LinkedIn inbox stuffed with SPAM.

If you intend to increase your reach, posting information about your product in an appropriate LinkedIn group is perfectly fine. The key is appropriate here - this is NOT trivial. Nobody wants to read a press release that states how great your product is! Instead, write about an interesting new product capability that attracts the attention of other group members. This way you will establish authority / reputation with your domain knowledge in a desired peer group.

I have absolutely removed people from my LinkedIn contacts for doing this - particularly if I know they couldn't pick me out of a police lineup (I don't know why I'm in a police lineup, just move on...).

That said, if it's 100% applicable to them, then it could be worth a very polite, very personal note asking if they would give you feedback. You know the saying... "Ask for money, get advice; ask for advice, get money."

Doing something like this is the fasted way to get removed from my contact/friend list.

It happened to me several times to get messages from (1st degree) Linkedin connections, that were clearly messages sent to all the person's connections. I really didn't mind : the messages had the right tone, with a personal touch, they were short, informative, one-time acts. So personally I think it's absolutely OK as long as it stays, as Hans pointed out, relevant and personal. I am considering using this technique myself later.