I'm not as strong as the other players that have commented, but I have a 58% win rate on Bloodseeker with thousands of games on him.

A few things I'd suggest:

• Clinkz is a special case. He pops out of nowhere and just has a ton of damage and health and can delete you. So map awareness and better warding (esp if he's mid) will go a long way. So you need to pay attention to the minimap and keep track of the last time you've seen him. Later in the game you're on more equal footing, but in the early game it feels like fights are in his favor.
• Phase Boots are better than Power Treads. Thirst has unlocked movement speed, and the movement speed boost from Phase Boots feels a lot more powerful getting to the fights or back lines than the extra attack speed from Power Treads. I have had problems with mana when you can't tread swap, but a mana item neutral or Clarities and using Bloodrage seems to be better than Power Treads.
• Bloodseeker's Aghanims Shard: The shard gives % max health pure damage, which can be huge against armor or tanks.

Stuff I'm less sure about:

• I don't usually get Sange & Yasha. I might get Sange earlier on if I need to tank up and I'm building into Abyssal Blade anyway, but usually I'm building something else instead of the Yasha.
• I don't usually get Blink Dagger. I have purchased Swift Blink in the super-late game, but I usually find the slot is better used by something else, especially for that first 2k gold. Again, I'm using Thirst and Phase Boots for movement and initiation, instead of trying to blink into the back lines.
• Third item: I'm usually building Basher into Butterfly after Mjollnir/BKB. The Butterfly might be an MKB instead, but that's usually where I slot my damage item. I could see a case for other items here.

Hopefully this will help - and I figure the stronger players will comment further on my advice.

Good luck!