Is there a site that charts total assets of a fund/ETF (GLD, UCO, etc)? I'd like to see total assets plotted over periods of time to get an idea if assets are increasing or decreasing.
My knowledge relates to ETFs only.
By definition, an ETF's total assets can increase or decrease based upon how many shares are issued or redeemed. If somebody sells shares back to the ETF provider (rather than somebody else on market) then the underlying assets need to be sold, and vice-versa for purchasing from the ETF provider. ETFs also allow redemptions too in addition to this.
For an ETF, to determine its total assets, you need to you need to analyze the Total Shares on Issue multipled by the Net Asset Value. ETFs are required to report shares outstanding and NAV on a daily basis.
"Total assets" is probably more a function of marketing rather than "demand" and this is why most funds report on a net-asset-value-per-share basis.
Some sites report on "Net Inflows" is basically the net change in shares outstanding multiplied by the ETF price.
If you want to see this plotted over time you can use a such as: http://www.etf.com/etfanalytics/etf-fund-flows-tool which allows you to see this as a "net flows" on a date range basis.