If you write to a member you are not friends with, you will have to wait for a reply.
This feature is there to protect the privacy of each individual member. Not only does this make it much more difficult for spammers and fakes to contact you, it also benefits you as a member.
Because how often does it happen that a user writes to you several times, but you are actually not interested in sending back even a "No, thanks"!
Of course, we strongly recommend that you at least reply with "No, thank you". Then your counterpart will know right away where he stands with you. A great thing that ensures that no one feels pressured anymore.
Small tip: Send the user a nice compliment or rate one of his pictures to facilitate the contact. You can also show your interest with a flirt ;-)