Start stripping, that will get EVERYONE's attention..

If you haven't brought it to his attention, I suggest you do that. He may not be doing it intentionally. He probably doesn't realize it. Maybe you could even join in since you're going with him anyway. It's not really fun for you to be there with his friends and not do anything. If you're friends with his friends, you might enjoy yourself more and not really realize that you're not getting the attention you're used to. You also have to realize that when he's with his friends, his focus is mainly on having a good time with them. Like I said, it's not really intentional. If he knows he's doing it and it's to the point where he totally forgets you exist, then I think you should reevaluate things.

Hope this helped.

Listen carefully. Remove every article of clothing you have on. Preferably slowly, but not necessary.

Probably just let him be with his friends?

flirt with his freinds

I wouldn't do anything. You'll just look needy. Let him have his boy time with his friends.

Everyone needs time for their friends so let him have it. He surely won't forget about you

Lol, just tell him how you feel. If he acts on what you say, then he's a keeper if not then i'm not sure the guys worth it. You could also maybe speak to his best friend if your on good terms with him.
Good luck.