There are a lot of image choices I would have changed if I were putting together this design with the intention to reflect a rounded/balanced 80's representation. Huey Lewis would be one I'd definitely include. As it stands, I don't think any of the silhouettes are of him.

Like Tony, I started to go backwards and picking artists to look for. Only to get frustrated of course.

Unfortunately, I also don't think the one with the keytar is anyone from Devo. I haven't seen any Devo images with a keytar yet, only strap mounted synth. Also haven't seen any with head-mounted mic. The suit also doesn't look like an outline of their bio suits to me and the belt looks a little low and not straight enough. Lastly, if I were designing the image and wanted to include Devo, it would be an image with their iconic red hats. Nothing else instantly says "Devo" IMO.

The following images are instantly recognizable:

Michael Jackson - the pose and the glove - it might as well be labled with his name in big bold letters.

Tina Turner - there just no mistaking that image for anyone else. The lean and the hair. And of course the legs.

Madonna - it's not the best silhouette, but still not really mistakable for anyone else. I'd have preferred a slightly different pose and perhaps more hair.

Cindy Lauper - also not mistakable even without any of the white parts. That dress and pose alone do it.

Boy George - hat and overall frumpiness of the outfit. This could not possibly be anyone else.

Prince - similar to the Michael Jackson, it might as well be labeled with his name - it wouldn't be any easier.

David Lee Roth - Jump. Period. I would *not* have put both Eddie Van Halen and David Lee Roth in the same image.

Everyone else is a little tougher, though a number of them now seem totally obvious, the above were the most in-your-face to me. I'd argue that the above are the most universally recognized ones too. Especially the MJ.

Anyway, I'm thinking of finding out where the designer lives and then holding him for ransom until he reveals all his sources.

Some other artists I considered in my backwards search:

Psychedelic Furs
Simple Minds
Thompson Twins
Spandau Ballet
Duran Duran
Yes
The Clash
Dire Straits (Tony mentioned lead singer as possibility for #20 in OP)
Men at Work
Frankie Goes to Hollywood

Some additional artists I'd consider back-searching:

Big Country
Bryan Adams
Rick Springfield
Peter Gabriel
Toto
Wham!/George Michael (maybe #28 for which I had already suggested Rick Astley)
Los Lobos (for 30/31 maybe)

#20 and #9 are probably the most generic ones of the lot, and it's easy to argue them as so many possibilities. Especially #20 IMO.