* Canwest pressured by debtload, advertising slump

* Company faces interest payment deadline Tuesday

* Shares tumble 22 percent (Adds details, updates stock. In U.S. dollars unless noted)

By Wojtek Dabrowski

TORONTO, April 13 (Reuters) - Shares of Canwest Global Communications CGS.TO are essentially worthless and should be avoided by investors as Canada's biggest media company fights to restructure its massive debt amid a severe advertising downturn, analysts said on Monday.

Canwest has another debt deadline on Tuesday, by which time it must pay $30.4 million in interest to holders of its 8 percent senior subordinated notes. The payment was originally due March 15, but the company missed it.

If it doesn't pay on Tuesday, the investors can demand the repayment of about $761 million of outstanding principal on the notes. This could further exacerbate the crisis facing the company.

"Given the significant liquidity challenges facing the company, we see no residual value in the shares of Canwest," BMO Capital Markets analyst Tim Casey wrote in a note to clients.

Canwest's shares fell 22 percent to close at 25 Canadian cents on the Toronto Stock Exchange -- a fresh year low for the stock.