Photoshop, web design motion graphics and publication all merge into 1 bigger category, you will find many people here only use photoshop as part of there bigger trade and you will find members here that only really use PS.
I believe what your after is an SEO specialist most web designers understand SEO and how to apply it to projects but SEO is only the technical side to what you are after, I think you really want to focus on graphics and slogans if you will to grab your viewers attention and make them want to read more into your cause. The SEO part will help towards getting traffic to your site But from there you need to have something visual to get them to stay there and draw them in. Without knowing what your cause is or what key words etc you want to promote then you are pretty much blocking yourself from getting help as it is rare that anyone with the skill set you require will read this and contact you, Mainly because the people you require will expect to get paid hundreds and maybe thousands of dollars for doing so, That said you may get people advertise themselves to you wanting to be paid that dont have the neccessary skill set you desire.
So my advise would be post some examples and people may offer you tips along the way, Or you may be better off approaching a reputable company to do all the work for you.
The question is how realistic are you is your site really going to be big enough to attract the people you are dreaming for or is this just somebody with an idea and dreaming.
The truth is if you want such specialist work doing then it is wasted if you are not doing your part.
Ie making your cause high profile
making sure you have your own domains and premium hosting
plenty of content for your site
a team of people behind you working on everything,
a premium website design not something done in an hour using notepad as the html editor.
You can have the best copywrite banner on the web optimised 100% but if you dont have a large following and the rest of the content needed to make it work then it is all wasted.
SEO these days is more than just embedding tags and naming components on your site to trick spiders into placing you higher on the search engine lists.
for example if your company is based in france your hosting is in England and your address is
www.anything.com Then you have just pretty much failed yourself getting high listings.
Now if you are based in France
your hosting company is in France
and you have an address like
www.anything.fr Then you have just got optimum results for that part of SEO
If you have to many keywords in your site then you will now score lower and get penalised as Google will detect it as you trying to trick Search Engines.
And now the biggest factor is traffic to your site and ratings if you dont get much traffic then you will list lower on search engines
If you get a lot of Google +1 ratings from many people then your site will be listed higher
if you get a lot of negative reviews then you will just drop off the list.
