Make sure the product or the content has market value. If you are a market leader, your product may not need much promotion. Nonetheless, getting an opinion leader for promotional purposes will indeed expedite the marketing campaign. The key here is to use the source appropriately. If you just need a media person for the sake of it, your customers may lose interest in your shallow promotional campaign. However, knowing that your product or content is worth supporting, you will have little problem selling it.
The best way to get influential people is to contact them or their managers via e-mail. Tweeting them for a request is not a wise option. Most of them receive dozens of requests each day and it is not appropriate to ask them for immediate favors.
If you are sending the product or delivering it in person, it is essential that you provide all relevant details of your product or content as most known people would like to use the product first before recommending it to others.
It is important to politely ask whether the person or celebrity will be able to help you out. In most scenarios, the answer will be in the negative but that doesn’t make him or her a jerk. You need to understand that celebrities continue to receive promotional goods on a regular basis, and may not be able to solely promote your product. There is nothing personal about it, and rather than taking it to heart, it is always good to either move on or wait for your turn. You may get lucky after all.