I would suggest to members to avoid filling this thread with several 'thank you' posts. A simple 'like' would serve the purpose and you could also post 'Thanks' to several members in one single post.
Just think - someone reaches a milestone - say 3000 posts. 15 people say 'congrats'. Then the person gives a party. Another 20 people say 'thanks for party'. Then the person who gave party posts 20 'thanks' for that. Don't you think this clutters the forum?
You can post several thanks in one post. A couple of people can post 'congrats' and the others can hit 'like'. If you very close friends or you are late and missed the post, you can send a PM or scrap.
Hope this is taken in the right spirit.