Send message programmatically

Hi … first of all thanks for this great plugin and the efforts you have done.

I had a query : I want to create a custom form on my page which will have some additional fields i require and will have the current user id and page author user id. When i click on submit for this form, it should programmatically send the “private message” from the current user to target user. Is there any available function like maybe “send_message($to_userid, $from_userid, $subject, $message_text)” which i can use to send the message and which will show up in the end-user message box? Hope you can understand my query!

Thanks,
Chris