You need to use capture groups, basically in a regex anything in brackets will be part of the cpature group, in this case you want to capture all the characters between two hashes. The any amount of characters regex is .* so this is what you want to capture between two hashes. Once you execute it you will find the match as second in the array (the first will be the string with the hashes.
var type = "";
var myString = "some text user#t12# some text";
var myRegexp = new RegExp(type+"#(.*)#","g");
var match = myRegexp.exec(myString);
alert(match[1]); // t12
any other matches between hashes will be in match[2].. match[n]
