Need help 13yr RAD?

Well, I have been reading the Foster message board everyday for weeks. I noticed the letters RAD was used a lot and I looked it up. I didn't think about it being something my kids would have but then last night I decided to look up the symptoms in detail because I have been having a lot of problems with my 13y son. My son wasn't in foster care. He is my adopted step son. I have been there since he turned 5. His bio mom left him in a baby swing day in and day out. He couldn't walked till 2.5 because his joints were not forming properly and needed crawling therapy. This alone makes me know that she did not take care of him when he was in her care. She has not seen him since he was almost 3. I have 2 older kids that had the same bio mom. I see a lot of symptoms of RAD in my youngest. However, he doesn't have all the symptoms. He does love affection and he has been a cuddler since 5. I know I need to get him to a behavior specialist. Is this something that is diagnosed or something that we know our kids have. He lies, steals, lacks cause and effect thinking, he had poor peer relationships, he steals and sneaks food he knows is not his and he doesn't seem to feel guilt. He does, however, make eye contact (with and with out lies) he is affectionate, he doesn't have a fascination with fire, and has never been cruel to animals. I am guessing has RAD and you don't need to have all the symptoms but I feel like he trusts us and I know that is a big one. What can I do to help him? All the nurturing techniques and things that I have read seem to be geared towards infants and I read there is little you can do when they hit puberty. Any help would be appreciated and I hope I can find help. Thank you so much!