Thank you for reaching out to us. As you said, your daughter is in a bad situation. As a parent, it is important for you to set strict limits and stay consistent with the consequences, no matter how hard she cries or yells at you. Do what you have set out to do by blocking her from communicating with the boy through social media sites like Facebook and on the phone. Her health and safety are your number one priority. She is only eleven, and she does not yet know what is best for her. At this point, getting along with your daughter should not be as important as teaching her to have proper boundaries with boys.
You also have an obligation to contact this boy's parents and explain to them what has happened. You may find them willing to help their son and cooperate with you, or you may find them uninterested and unmotivated to help. Either way, you have at least contacted them and put the information out there for them to handle with their child. Hopefully they will be proactive and put an end to the texting and to the unhealthy relationship with your daughter. Most parents would want to know if their teenager was trying to have sexual contact with a younger child, and would take action to get their child's behavior under control.
We would like you to call our hotline and speak with a parenting counselor about this in more detail, to give you the best help possible. Please call us toll-free at 1-800-448-3000. We are here 24/7 for parents and kids of all ages. Thanks again for reaching out. We look forward to hearing back from you soon.