Simply begin your tweet with their username (@username). This also works for people you aren't following.
If someone that DOES follow you retweets you and someone sees that tweet on their TL they will RT you.. and they don't have to be following you... Follow me @ALexisU_
Tweet them.
When you send a tweet to someone who doesn't follow you, they can still see your tweet if their privacy settings allow it. However, it will not appear in their notifications unless they specifically check your profile or if you mention them using an "@" in your tweet. Additionally, if their account is set to private, they will not see your tweet at all.
Send them a tweet and ask them nicely.
By clicking on 'reply' or starting a tweet from scratch and starting it with their username (@username).
Yes you can still tweet them and they will still see the tweet in their mentions.
You can't make someone follow you. If you want him to follow you then you should tweet him and ask him to do so.
You can tweet someone even if their account is protected.
This is not possible, try asking the person with a tweet (to send a message directly to someone type @<twittername> before your tweet, however it will still be public, I think). To request to follow someone with a private account, click on follow and a message will be sent to them to either accept or deny your request.
You receive a tweet when someone mentions you in their tweet.
In order to direct message someone they must follow you, and you must follow them. If this is the case, simply type D:theirtwittername and then your message or question??! send it to 40404.
Begin your tweet with their username (@username)