Similar problem with How to use sbt behind authenticated proxy?. I tried with the given answer and problem still there.
When I run sbt in terminal, it
It's quite a late answer, but I encountered the same problem working behind a proxy. If this is your case, you should run export JAVA_OPTS="$JAVA_OPTS
-Dhttp.proxyHost= before running sbt.
If you are still unsure if it's going ahead with the downloading, you should try launching sbt with the verbose option sbt -v, as suggested by @evan912. If you had a problem with the proxy, after setting it you should see some [info] downloading logging on your console.