I would recommend placing a personal ad in Anchorage newspapers. Unless your brother & other relatives are themselves interested in genealogy, they are more likely to learn of your query through ads in general circulation newspapers (or through friends who read the ads) than on a genealogical website.

The Anchorage Daily News <http://www.adn.com/>;, besides being the largest newspaper in the state, also has a statewide circulation. There's a decent listing, with links, of other Alaska newspapers at <http://justice.uaa.alaska.edu/refrenz/news.html>;. Anchor Point is on the Kenai Peninsula near Homer, so the Homer newspaper & other Kenai Peninsula newspapers (Soldotna, Kenai) or papers for fishing towns might also be good (e.g., Dutch Harbor, Kodiak, Valdez, Cordova).

Best of luck in finding your brother.

-- Mel